oversight

Highway Safety: Research Continues on a Variety of Factors That Contribute to Motor Vehicle Crashes

Published by the Government Accountability Office on 2003-03-31.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

             United States General Accounting Office

GAO          Report to Congressional Requesters




March 2003
             HIGHWAY SAFETY

             Research Continues
             on a Variety of
             Factors That
             Contribute to Motor
             Vehicle Crashes




GAO-03-436
                                                March 2003


                                                HIGHWAY SAFETY

                                                Research Continues on a Variety of
Highlights of GAO-03-436, a report to           Factors That Contribute to Motor Vehicle
congressional requesters
                                                Crashes



Nearly 6.3 million motor vehicle                Many factors combine to produce circumstances that may lead to a
crashes occurred in the United                  motor vehicle crash—there is rarely a single cause of such an event.
States in 2001, or one crash every 5            Three categories of factors contribute to crashes: human factors,
seconds. On average, a person was
injured in these crashes every 10
                                                roadway environment factors, and vehicle factors. Human factors
seconds, and someone was killed                 involve the actions taken by or the condition of the driver of the
every 12 minutes. Since the 1970s,              automobile, including speeding and violating traffic laws, as well as being
progress has been made in                       affected by alcohol or drugs, inattention, decision errors, and age.
reducing the number of fatalities               Roadway environment factors include the design of the roadway,
and injuries on our nation’s roads.             roadside hazards, and roadway conditions. Vehicle factors include any
From 1975 through 2001, fatalities              failures that may exist in the automobile or design of the vehicle. Human
decreased from 44,525 to 42,116,
                                                factors are seen as the most prevalent, according to data, experts, and
while the rate of fatalities per 100
million vehicle miles traveled                  studies, in contributing to crashes, followed by roadway environment
decreased from 3.35 to 1.51.                    and vehicle factors.
However, the decline in fatalities
has leveled off in recent years. In             Agencies within the Department of Transportation have research
the 1970s, Indiana University                   projects underway or planned that address the factors that contribute to
conducted one of the most                       crashes. For example, the Federal Motor Carrier Safety Administration
significant studies to date on the              and the National Highway Traffic Safety Administration are conducting a
factors that contribute to motor
vehicle crashes. This study                     study on the causes and contributing factors to large truck crashes. In
examined human, environmental,                  addition, the National Highway Traffic Safety Administration is
and vehicle factors that contribute             conducting a 100-Car Naturalistic Driving Study and the Drive Atlanta
to crashes. As requested, this                  Study. The 100-Car Naturalistic Driving Study involves collecting data
report provides more recent                     from vehicles equipped with sensors and cameras to obtain better
information from data, experts, and             information on crashes and near misses. The Drive Atlanta Study
studies about the factors that                  involves collecting data from 1,100 vehicles equipped with data recorders
contribute to motor vehicle crashes
and information about major                     to develop information about how excessive speed contributes to
ongoing and planned Department                  crashes. In addition, the Transportation Research Board has proposed a
of Transportation research into                 broad, 6-year, $180 million research program focused on making
factors that contribute to crashes.             significant improvements in highway safety. This study, among other
                                                things, would involve installing sensors and other data collection devices
                                                on over 5,000 vehicles.

                                                Fatality Statistics, 1975–2001




www.gao.gov/cgi-bin/getrpt?GAO-03-436

To view the full report, including the scope
and methodology, click on the link above.
For more information, contact Peter Guerrero,
(202) 512-2834, guerrerog@gao.gov.
Contents


Letter                                                                                     1
               Results in Brief                                                            2
               Background                                                                  3
               Human, Roadway Environment, and Vehicle Factors Contribute to
                 Motor Vehicle Crashes                                                     6
               Federal Research Directed at Better Understanding of Factors That
                 Contribute to Crashes                                                   32
               Agency Comments and Our Evaluation                                        36

Appendix I     Objectives, Scope, and Methodology                                        38
               Analyzing NHTSA Data                                                      38
               Identifying Studies                                                       40
               Interviewing Federal Officials and Experts                                41
               Ongoing and Planned Transportation Research                               41

Appendix II    Tri-Level Study of the Causes of Traffic Accidents                        42
               Objectives, Scope, and Methodology for the Tri-Level Study                42
               Results of the Tri-Level Study                                            43

Appendix III   Roadway Design Features                                                   46



Figures
               Figure 1: Fatality Statistics, 1975–2001                                    4
               Figure 2: Crash Causes Found by the Tri-Level Study                         5
               Figure 3: Speeding Drivers in Fatal Crashes, by Age and Gender,
                        1997–2001                                                          8
               Figure 4: Drivers in Alcohol-Related Fatal Crashes, by Age and
                        Gender, 1997–2001                                                12
               Figure 5: Inattentive Drivers Involved in Crashes by Age, 1997–2001       15
               Figure 6: Number and Rate of Driver Involvement in Fatal Crashes
                        by Age, 1997–2001                                                18
               Figure 7: Fatality Rates by Type of Road System, 2001                     22
               Figure 8: Vehicle Crash Rates, 2001                                       29
               Figure 9: Passenger Vehicle Rollovers, 2001                               30
               Figure 10: Factors Contributing to Crashes Identified by the Tri-
                        Level Study                                                      44
               Figure 11: Impact of Access Points on Traffic Crashes                     50




               Page i                                     GAO-03-436 Traffic Crash Causation
Abbreviations

AAA               former American Automobile Association
AASHTO            American Association of State Highway and Transportation
                   Officials
BAC               blood alcohol content
CDS               Crashworthiness Data System
DOT               Department of Transportation
FARS              Fatality Analysis Reporting System
FHWA              Federal Highway Administration
FMCSA             Federal Motor Carrier Safety Administration
F-SHRP            Future Strategic Highway Research Program
GES               General Estimates System
NHTSA             National Highway Traffic Safety Administration
SUV               sport utility vehicle
VMT               vehicle miles traveled




This is a work of the U.S. Government and is not subject to copyright protection in the
United States. It may be reproduced and distributed in its entirety without further
permission from GAO. It may contain copyrighted graphics, images or other materials.
Permission from the copyright holder may be necessary should you wish to reproduce
copyrighted materials separately from GAO’s product.




Page ii                                              GAO-03-436 Traffic Crash Causation
United States General Accounting Office
Washington, DC 20548



                                   March 31, 2003

                                   The Honorable Carl Levin
                                   United States Senate

                                   The Honorable George V. Voinovich
                                   United States Senate

                                   Nearly 6.3 million motor vehicle crashes occurred in the United States in
                                   2001, or one crash every 5 seconds. On average, a person was injured in
                                   these crashes every 10 seconds, and someone was killed every 12 minutes.
                                   While there have been significant improvements in motor vehicle safety
                                   over the past several decades, decreases in injuries and fatalities have
                                   leveled off since the early 1990s.

                                   In the 1970s, Indiana University conducted a major study that examined
                                   the human, environmental, and vehicle factors that contribute to traffic
                                   crashes.1 You asked us to (1) provide more recent information on the
                                   factors that contribute to motor vehicle crashes, and (2) identify major
                                   ongoing and planned Department of Transportation research into factors
                                   that contribute to crashes.

                                   To provide information on factors that contribute to motor vehicle
                                   crashes, we obtained and analyzed crash data from three Department of
                                   Transportation databases. In addition, we interviewed experts from
                                   academia, insurance organizations, and advocacy groups. To identify
                                   recent studies on factors that contribute to motor vehicle crashes, we
                                   conducted a literature search, explored the Transportation Research
                                   Information System, and reviewed periodicals. This effort resulted in
                                   numerous studies being identified on various aspects of motor vehicle
                                   crashes. We then, with input from a number of experts and agency
                                   officials, judgmentally selected studies that would provide additional
                                   information on the particular factors being discussed. For each of the
                                   selected studies that are used in this report, we determined whether the
                                   studies’ findings were generally reliable. We evaluated the methodological
                                   soundness of the studies using common social science and statistical
                                   practices. To identify the major ongoing and planned research into factors



                                   1
                                    J.R. Treat et al., Tri-Level Study of the Causes of Traffic Accidents (Washington, D.C.:
                                   Institute for Research in Public Safety, May 30, 1979), for the U.S. Department of
                                   Transportation.



                                   Page 1                                                GAO-03-436 Traffic Crash Causation
                   that contribute to crashes, we interviewed officials from the National
                   Highway Traffic Safety Administration, the Federal Highway
                   Administration, and the Transportation Research Board. Appendix I
                   provides more details on our scope and methodology.


                   Many factors can combine to produce circumstances that lead to a motor
Results in Brief   vehicle crash—there is rarely a single cause of such an event. Three
                   categories of factors contribute to crashes: human factors, roadway
                   environment factors, and vehicle factors. Human factors involve the
                   actions taken by or the condition of the driver of the motor vehicle,
                   including speeding and violating traffic laws, as well as being affected by
                   alcohol or drugs, inattention, decision errors, and age. Roadway
                   environment factors that contribute to, or are associated with, crashes
                   include the roadway design (for example, medians, narrow lanes, the lack
                   of shoulders, curves, access points, or intersections); roadside hazards
                   (for example, poles, trees, or embankments adjacent to the road); and
                   roadway conditions (for example, rain, ice, snow, or fog). Vehicle factors
                   include any vehicle-related failures that may exist in the automobile or
                   design of the vehicle. In general, human factors are considered to be the
                   most prevalent factors contributing to crashes, followed by roadway
                   environment and vehicle factors.

                   Various agencies within the Department of Transportation have research
                   projects underway or planned that address the factors that contribute to
                   crashes. For example, the Federal Motor Carrier Safety Administration
                   and the National Highway Traffic Safety Administration are studying the
                   causes of, and factors contributing to, large truck crashes. In addition, the
                   National Highway Traffic Safety Administration’s 100-Car Naturalistic
                   Driving Study involves collecting data from vehicles equipped with sensors
                   and cameras to obtain better information on crashes and near misses.
                   Another project, the Drive Atlanta Study, involves collecting data from
                   1,100 vehicles equipped with data recorders to develop information about
                   how speeding contributes to crashes. A number of follow-on studies to
                   these efforts are also being considered. In addition, the Transportation
                   Research Board has proposed a broad, 6-year, $180 million research
                   program focused on making significant improvements in highway safety.
                   This program, among other things, could involve installing sensors and
                   other data collection devices on over 5,000 vehicles. The final phase of the
                   research program would use the results of the instrumented vehicle study
                   to identify countermeasure improvements.




                   Page 2                                       GAO-03-436 Traffic Crash Causation
             We provided copies of a draft of this report to the Department of
             Transportation for its review and comment. In discussing this report,
             agency officials provided technical clarification and information, which we
             incorporated in the report as appropriate. In addition, National Highway
             Traffic Safety Administration officials provided information comparing
             light truck and passenger car crash rates, which we also incorporated in
             the report.


             Since the 1970s, progress has been made in reducing the number of
Background   fatalities and injuries on our nation’s roads, but the numbers are still
             significant. From 1975 through 2001, annual fatalities decreased from
             44,525 to 42,116, or about 5 percent. During the same period, the fatality
             rate per 100 million vehicle miles traveled, a common method of
             measurement, dropped from 3.35 to 1.51, or about 55 percent. This
             reduction in fatalities was considerable, given the growth in the number of
             drivers and vehicles on the road. For example, from 1975 through 2001,
             licensed drivers increased from about 130 million to about 191 million, and
             the number of registered vehicles increased from about 126 million to
             about 221 million. Figure 1 shows the yearly number of fatalities and the
             rate of fatalities per 100 million vehicle miles traveled. Injury and property-
             damage-only crashes also fell, going from about 6.8 million in 1988, the
             earliest year of available data, to about 6.3 million in 2001.




             Page 3                                        GAO-03-436 Traffic Crash Causation
Figure 1: Fatality Statistics, 1975–2001




                                           The fatal, injury, and property-damage-only crashes have significant
                                           economic cost. The National Highway Traffic Safety Administration
                                           (NHTSA) recently calculated the economic costs for motor vehicle crashes
                                           in 2000 at more than $230 billion, or the equivalent of over $800 for every
                                           person living in the United States. NHTSA’s estimate of economic costs
                                           includes productivity losses, property damage, medical costs,
                                           rehabilitation costs, travel delay, legal and court costs, emergency
                                           services, insurance administration costs, and costs to employers.

                                           One of the most significant studies to date on the factors that contribute to
                                           motor vehicle crashes was the Tri-Level Study of the Causes of Traffic
                                           Accidents, conducted in the 1970s by the Indiana University at
                                           Bloomington Institute for Research in Public Safety. Referred to as the Tri-
                                           Level study, it investigated how frequently various factors contributed to
                                           traffic crashes. According to NHTSA officials, the Tri-Level study has been
                                           the only study in the past 30 years to collect large amounts of on-scene
                                           crash causation data. To provide researchers with insight into the factors
                                           that contribute to traffic crashes, collision data were collected on three
                                           levels, each providing an increasing level of detail, including 13,568 police-
                                           reported crashes; 2,258 crashes investigated by on-scene technicians; and
                                           420 crashes investigated in depth by a multidisciplinary team. The study
                                           assessed causal factors as either definite, probable, or possible. The study
                                           found that crashes were caused by human (or driver-based) factors,



                                           Page 4                                       GAO-03-436 Traffic Crash Causation
environmental (roadway or weather-related) factors, or vehicle-related
factors. As shown in figure 2, the study concluded that the human factors
were definite or probable causes in about 93 percent of crashes, while
environmental and vehicle factors contributed to about 33 and 13 percent,
respectively. See appendix II for a more detailed discussion of the Tri-
Level study.

Figure 2: Crash Causes Found by the Tri-Level Study




NHTSA’s mission is to reduce deaths, injuries, and economic losses
resulting from motor vehicle crashes. As part of this responsibility, NHTSA
conducts or sponsors research into the causes of motor vehicle crashes.
NHTSA also conducts research on driver behavior and traffic safety to
develop more efficient and effective means to improve safety. Three
principal databases provide information about traffic crashes: the Fatality
Analysis Reporting System (FARS), the Crashworthiness Data System
(CDS), and the General Estimates System (GES). The FARS database
contains information provided by the states on all vehicle crashes that
result in the death of an occupant or nonmotorist within 30 days of the




Page 5                                         GAO-03-436 Traffic Crash Causation
                      incident. The CDS database contains information from a detailed sample
                      of about 4,000 minor, serious, or fatal tow-away crashes, annually. To
                      obtain this information, teams of trained crash investigators visit the crash
                      site and collect data on such elements as the damage to the vehicle and
                      interior locations struck by the occupants. The GES database contains
                      information from a nationally representative sample of police accident
                      reports. This is NHTSA’s largest crash database, with information
                      collected on over 50,000 crashes each year.

                      The Federal Highway Administration’s (FHWA) safety mission is to reduce
                      highway fatalities and injuries through development and implementation
                      of a program of nationally coordinated research and technology
                      innovations. Research is conducted in areas that address FHWA’s highway
                      safety goals related to roadway departure, intersections, and pedestrians.
                      FHWA is also conducting research in a number of areas that will partially
                      focus on crash causation, including rollovers, speed management,
                      intersection safety, and pedestrian and bicyclist safety. FHWA annually
                      produces a highway statistics report, which consists of data on motor fuel,
                      motor vehicles, driver licensing, highway-user taxing, state and local
                      government highway finance, highway mileage, and federal aid for
                      highways. FHWA also maintains a database, called the Highway Safety
                      Information System. The system uses data on crash, roadway, and traffic
                      variables collected by eight states to analyze a number of highway safety
                      problems. These analyses range from identifying basic problems, to
                      identifying the size and extent of a safety issue, to modeling efforts that
                      attempt to predict future crashes from roadway characteristics and traffic
                      factors.


                      Motor vehicle crashes are complex events that rarely have a single cause.
Human, Roadway        For example, it would be challenging to identify a single cause of a crash
Environment, and      that occurred on a narrow, curvy, icy road when an inexperienced driver,
                      who had been drinking, adjusted the radio or talked on a cell phone. It
Vehicle Factors       would likely be the combined effect of a number of these factors that
Contribute to Motor   contributed to the crash.
Vehicle Crashes       In examining the causes of motor vehicle crashes, a number of experts and
                      studies identified three categories of factors that contribute to crashes—
                      human, roadway environment, and vehicle factors. Human factors involve
                      the actions taken by or the condition of the driver of the automobile,
                      including speeding and other traffic violations, as well as the effects of
                      alcohol or drugs, inattention, decision errors, and age. Roadway
                      environment factors that contribute to or are associated with crashes


                      Page 6                                       GAO-03-436 Traffic Crash Causation
                           include the design of the roadway (for example, medians, lane width,
                           shoulders, curves, access points, or intersections); roadside hazards (for
                           example, poles, trees, or embankments adjacent to the road); and the
                           roadway conditions (for example, rain, ice, snow, or fog). Vehicle factors
                           include vehicle-related failures and vehicle design issues that contribute to
                           a crash. In general, human factors are considered to be the most prevalent
                           factor contributing to crashes, followed by roadway environment and
                           vehicle factors. Although this report discusses these categories separately,
                           they should be viewed in terms of how they can concurrently contribute to
                           an unstable situation that results in a crash.


Human Factors Contribute   Human factors involve actions taken by or the condition of the driver of
to Motor Vehicle Crashes   the vehicle. They are considered the most prevalent factors by data,
                           experts, and studies in traffic crashes. Human factors that can contribute
                           to crashes include speeding and other traffic violations, as well as the
                           effects of alcohol or other drugs, inattention, driver decision errors, and
                           age.

Speeding                   Driving either faster than the posted speed limit or faster than conditions
                           would safely dictate can contribute to traffic crashes. Speeding reduces a
                           driver’s ability to steer safely around curves or objects in the roadway,
                           extends the distance necessary to stop a vehicle, and increases the
                           distance a vehicle travels while the driver reacts to a dangerous situation.

                           According to our analysis of NHTSA’s databases, from 1997 through 2001,
                           speeding was identified as a contributing factor in about 15 percent of all
                           crashes and about 30 percent of all fatal crashes. In addition, almost 64,000
                           lives were lost in speeding-related crashes.2 As shown in figure 3, we found
                           that for every age category of drivers involved in fatal crashes, males were
                           more likely than females to be involved in a fatal speed-related crash. In
                           addition, younger drivers, regardless of sex, are the most likely to be
                           involved in a speed-related fatality. From 1997 through 2001, 36 percent of
                           male drivers and 24 percent of female drivers 16 to 20 years old who were
                           involved in fatal crashes were speeding at the time of the crash. The




                           2
                            NHTSA defines a crash as speed-related if the driver was charged with a speed-related
                           offense or if an officer indicated that the driver was racing, driving too fast for conditions,
                           or exceeding the posted speed limit.




                           Page 7                                                  GAO-03-436 Traffic Crash Causation
percentage of speeding-related fatal crashes decreases with increasing
driver age.3

Figure 3: Speeding Drivers in Fatal Crashes, by Age and Gender, 1997–2001




A 1998 study by NHTSA and FHWA indicates that fatal crashes increased
in states that raised speed limits.4 When Congress enacted the National
Highway System Designation Act of 1995 (P.L. 104-59), which repealed the
national maximum speed limit, the Secretary of Transportation was
required to study the impact of states’ actions to raise speed limits above




3
 Some analyses in this report discuss fatality data associated with specific factors. It should
be noted that other elements, in addition to the factor discussed, might have also
contributed to the fatalities. These would include circumstances such as the use of safety
belts or other occupant protection measures.
4
NHTSA/FHWA, Report to Congress: The Effect of Increased Speed Limits in the Post-
NMSL Era (Washington, D.C.: February 1998).




Page 8                                                 GAO-03-436 Traffic Crash Causation
55 and 65 miles per hour. The study found that states with increased speed
limits in 1996 experienced approximately 350 more Interstate fatalities
than would have been expected based on historical trends—about 9
percent above expectations. Concurrently, the Interstate fatalities
experienced in states that did not increase speed limits in 1996 were
consistent with pre-1996 trends. The Insurance Institute for Highway
Safety also assessed the effects of speed limit increases.5 Its researchers
found an increase in fatalities for a 9-month period in 1996 on Interstate
highways and freeways, as compared with the previous 6 years—about 16
percent in 12 of the states that had raised maximum speed limits to at least
70 miles per hour by March 1996. In contrast, occupant fatalities increased
only 4 percent on Interstate highways and freeways in the comparison
group of states that did not raise speed limits. However, both of these
studies are limited because they cover short time periods.

According to a Transportation Research Board official, studies have
confirmed a direct relationship between speed and crash severity.6 Once a
crash has occurred—that is, a vehicle has hit another vehicle or a
stationary object—the vehicle undergoes a rapid change in speed. While
the vehicle decelerates rapidly, its occupants continue to move at the
vehicle’s speed prior to impact until they are stopped by striking the
interior of the vehicle, by impact with objects external to the vehicle if
ejected, or by being restrained by a safety belt or an airbag that deploys.

According to the FHWA Director of the Office of Safety Programs, while
absolute speed clearly relates to injury and fatality outcomes, speeding is
the real issue. The Director pointed out that despite their lower volumes,
almost half of all speeding-related fatalities occur on local or collector
roads—low-speed roads found in residential and business areas. In
addition, the Director said that speed variance is also a factor. When
vehicles driving down a particular roadway are traveling at very different
speeds, the probability of a crash increases. The relative crash-
involvement rate increases for vehicles that are traveling above or below
the average speed of traffic.


5
 Charles M. Farmer, Richard A. Retting, and Adrian K. Lund, Effect of 1996 Speed Limit
Changes on Motor Vehicle Occupant Fatalities (Washington, D.C.: Insurance Institute for
Highway Safety, October 1997). This study focused on 12 states that raised maximum speed
limits to at least 70 miles per hour between December 8, 1995, and April 1, 1996.
6
 The Transportation Research Board is a unit of the National Research Council, a private,
nonprofit institution that is the principal operating agency of the National Academy of
Sciences and the National Academy of Engineering.




Page 9                                               GAO-03-436 Traffic Crash Causation
Traffic Control Violations   Drivers who fail to follow prescribed traffic control laws also contribute to
                             crashes. This includes running red lights or failing to stop at stop signs.
                             Our analysis of NHTSA’s data found that from 1997 through 2001, about 36
                             percent of motor vehicle crashes occurred at traffic control devices. Of
                             those crashes, 59 percent occurred at traffic lights while an additional 28
                             percent occurred at stop signs.

                             A study performed by the Insurance Institute for Highway Safety and the
                             Preusser Research Group identified characteristics of red light–running
                             crashes and the drivers involved.7 It found that drivers’ noncompliance
                             with traffic control devices, such as traffic signals and stop signs, is a
                             major cause of motor vehicle crashes. The study examined the prevalence
                             of red light–running crashes on a national basis to identify the
                             characteristics of such crashes and the drivers involved.8 The study
                             estimated that almost 260,000 red light-running crashes occurred in 1996,
                             of which 809 resulted in fatalities. It also found that, as a group, red light
                             runners involved in crashes were more likely than other drivers to be
                             younger than age 30, to be male, to have prior moving violations and
                             convictions for driving while intoxicated, to have invalid driver’s licenses,
                             and to be reported by police as having consumed alcohol prior to the
                             crash.

                             According to an official from Northwestern University, red light–running
                             might also partly reflect driver frustration with poor traffic operations. For
                             example, a driver might feel the need to speed through a red light because
                             of previous experience of being held at that light too long, or of being
                             subjected to a series of unsynchronized stop lights. A 1999 study funded by
                             DaimlerChrysler Corporation surveyed over 5,000 people regarding their
                             behavior at red lights.9 The study found that those respondents who
                             reported speeding up to beat a red light would most often do so because
                             they were in a rush and wanted to save time.



                             7
                              Richard A. Retting and Allan F. Williams for the Insurance Institute for Highway Safety,
                             and Robert G. Ulmer for the Preusser Research Group, “Prevalence and Characteristics of
                             Red Light Running Crashes in the United States,” Accident Analysis and Prevention, vol.
                             31 (1999), pp. 687–94.
                             8
                              The study reviewed intersection crashes in both the Fatality Analysis Reporting System
                             and the General Estimates System during the 5-year period from 1992 through 1996.
                             9
                              Bryan E. Porter, Thomas D. Berry, Jeff Harlow, and Tancy Vandecar, A Nationwide
                             Survey of Red Light Running: Measuring Driver Behaviors for the “Stop Red Light
                             Running” Program, June–August 1999.




                             Page 10                                              GAO-03-436 Traffic Crash Causation
Alcohol and Other Drugs   Alcohol and other drugs are contributing factors in many motor vehicle
                          crashes. It is illegal in every state and the District of Columbia to drive a
                          motor vehicle while under the influence of, impaired by, or with a specific
                          blood content of alcohol or drugs. In addition, all states but Massachusetts
                          have blood alcohol laws that make it illegal to drive with a specified level
                          of alcohol in their blood.10 As of January 2003, 17 states had set the
                          standard at .10 percent blood alcohol content (BAC)—the level at which a
                          person’s blood contains 1/10 of 1 percent alcohol.11 The remaining states
                          have more stringent laws, setting the limit at .08 percent BAC. According
                          to NHTSA, on average, a 170-pound man reaches .08 percent BAC after
                          consuming five 12-ounce beers (4.5 percent alcohol by volume) over a 2-
                          hour period. A 120-pound woman reaches the same level after consuming
                          three beers over the same period.

                          In analyzing NHTSA’s databases, we found that from 1997 through 2001,
                          there were about 76,000 alcohol-related fatal crashes (41 percent of all
                          fatal crashes), 980,000 alcohol-related injury crashes (10 percent of all
                          injury crashes), and 2.3 million alcohol-related crashes (7 percent of all
                          crashes).12 During this 5-year period, nearly 85,000 people died in alcohol-
                          related crashes. Eighty-six percent of these fatalities occurred in crashes
                          where the highest recorded BAC was .08 percent or above, while 14
                          percent occurred in crashes where the highest recorded BAC was between
                          .01 percent and .07 percent. In addition, we found that male drivers were
                          more likely to be involved in alcohol-related fatal crashes than female
                          drivers. Figure 4 shows that, for each age category, there were a greater
                          number of male than female drivers in fatal crashes that involved alcohol.




                          10
                           Blood alcohol content of .08 percent in Massachusetts is evidence of alcohol impairment,
                          but it is not illegal per se.
                          11
                           Of these states, Louisiana, New York, and Tennessee have .08 percent BAC laws that will
                          be effective during the latter half of 2003.
                          12
                           NHTSA indicates that a fatality is alcohol-related if it occurred in a crash where any one
                          of the actively involved persons in the crash had a BAC of .01 percent or greater.




                          Page 11                                               GAO-03-436 Traffic Crash Causation
Figure 4: Drivers in Alcohol-Related Fatal Crashes, by Age and Gender, 1997–2001




While research has shown that everyone’s driving is impaired at blood
alcohol levels of .10 percent and higher, recent research has shown that
lower levels of alcohol also affect performance. In a study by the Southern
California Research Institute, 168 test subjects were tested at zero BAC;
then at the highest BAC for their drinking classification of either light,
moderate, or heavy drinker; and then at .02 percent BAC intervals, as their
alcohol levels decreased.13 For this study, the researchers defined
impairment by comparing the subjects’ performance on a given test while
under the influence of alcohol versus their performance on the same test
after being given a placebo. According to the resulting report, alcohol
impaired the driving-related skills for these volunteers at .02 percent BAC,




13
  H. Moskowitz, M. Burns, D. Fiorentino, A. Smiley, and P. Zador, Driver Characteristics
and Impairment at Various BACs (Los Angeles, CA: Southern California Research
Institute, August 2000).




Page 12                                              GAO-03-436 Traffic Crash Causation
the lowest tested alcohol level. The magnitude of impairment increased
consistently at BACs through .10 percent, the highest level tested.14
According to a Southern California Research Institute official, this study is
significant because it provided important, previously unknown findings
that certain driving-related skills are impaired at any departure from zero
BAC.

A recent study by Westat examined the relative risk of fatal crash
involvement as a function of the BAC of fatally injured or surviving
drivers.15 By combining crash data from FARS with exposure data from the
1996 National Roadside Survey, the researchers determined that, in
general, the relative risk of involvement in a fatal passenger vehicle crash
increased steadily with increased driver’s BAC.16 For example, the study
found that a .02 percent BAC increase among 16-through-20-year-old male
drivers was estimated to more than double the relative risk of a fatal
single-vehicle crash injury. The study also found that among drivers aged
21 through 34, those with a BAC of .03 percent have twice the risk of
fatalities as compared with drivers with zero BAC. Furthermore, among
drivers aged 21 through 34, those with a BAC of .10 percent have over 10
times the risk of a fatality compared with drivers with zero BAC.

All states restrict driving while under the influence of, being impaired by,
or being incapable of safely driving because of illegal drugs or prohibited
substances in the driver’s body. As of January 2003, eight states have
statutes that make it unlawful for a driver to have any amount of an illegal
drug or prohibited substance in his or her body while operating a motor
vehicle, regardless of how the drug affects the driver’s driving ability.17



14
 The study subjects were examined only as their BAC was declining and, according to the
study, the results would underestimate the magnitude of impairment expected during
alcohol consumption when BAC was rising.
15
 P.L. Zador, S.A. Krawchuk, and R.B. Voas, Relative Risk of Fatal Crash Involvement by
BAC, Age and Gender (Rockville, MD: Westat, April 2000).
16
  The 1996 National Roadside Survey was a national survey of weekend, nighttime drivers
in the 48 contiguous states. The survey consisted of interviewing and breath-testing over
6,000 noncommercial four-wheel vehicle operators between September and November
1996.
17
  These eight states include Arizona, Georgia, Indiana, Illinois, Iowa, Minnesota, Rhode
Island, and Utah. The Georgia Supreme Court has determined that the Georgia statute, Ga.
Code Ann. 40-6-391(a)(6) (2002), is an unconstitutional denial of equal protection. See Love
v. State, 271 Ga. 398 (1999). Accordingly, the enforceability of the Georgia statute is
questionable.




Page 13                                               GAO-03-436 Traffic Crash Causation
                     Additional states have varying legislation that also allows zero tolerance to
                     driving under the influence of drugs.18

                     Studies have shown that drugs can affect driving-related skills. For
                     example, a study by Maastricht University, the Netherlands, indicated that
                     the combined use of marijuana and alcohol impairs driving performance.19
                     For a small number of subjects who were somewhat frequent users of
                     marijuana, the study found that either marijuana doses alone or alcohol
                     alone impaired the subjects’ test-driving performances. However, subjects
                     who used marijuana in combination with alcohol demonstrated
                     impairment in several aspects of driving performance. Another study by
                     Maastricht University also found the combined use of marijuana and
                     alcohol to produce similar effects on a small, limited group of subjects.
                     The study showed that under the influence of low doses of either
                     marijuana or alcohol, the drivers were less able to detect peripheral traffic
                     and instead focused on the central driving task.20

Driver Inattention   Driver inattention occurs when there is a delay in recognition of
                     information needed to safely accomplish the driving task. Two categories
                     of driver inattention are distraction and drowsiness. Drivers may become
                     distracted when they direct their attention elsewhere because of some
                     occurrence inside or outside of the vehicle. NHTSA defines four categories
                     of distraction: visual distraction (for example, looking away from the
                     roadway), auditory distraction (for example, responding to a noise, such
                     as a ringing cell phone), biomechanical distraction (for example, manually
                     adjusting the radio volume), and cognitive distraction (for example, being
                     lost in thought). Many distracting activities that drivers engage in can
                     involve more than one of these components. Driver drowsiness is also a
                     type of driver inattention, in that a tired or fatigued driver may exhibit
                     behaviors typically associated with inattentive drivers.


                     18
                      Examples of zero tolerance to driving under the influence of drugs include laws that
                     prohibit drug addicts or habitual users of drugs from driving vehicles (found in California,
                     Colorado, Idaho, Kansas, and West Virginia) or statutes that make it illegal for minors to
                     drive with any amount of a prohibited drug in their bodies (found in North Carolina and
                     South Dakota).
                     19
                      Hindrik W. J. Robbe and James F. O’Hanlon, Marijuana, Alcohol, and Driving
                     Performance (The Netherlands: Institute for Human Psychopharmacology, July 1999).
                     20
                      C.T.J. Lamers and J.G. Ramaekers, Visual Search and Urban City Driving under the
                     Influence of Marijuana and Alcohol (The Netherlands: Maastricht University, June 2001).
                     Specifically, both studies examined the effects of delta-9-tetrahydrocannabinol (THC), the
                     primary active ingredient of cannabis (marijuana).




                     Page 14                                                GAO-03-436 Traffic Crash Causation
Our analysis of 1997 through 2001 data from NHTSA found that, overall,
about 2.5 million drivers of passenger vehicles that were towed away from
crashes were identified as inattentive. Of these, about 1.3 million were
distracted, about 871,000 “looked but did not see” (an aspect of being
inattentive), and about 348,000 were sleepy or asleep. In addition, about
7.6 million drivers were identified as “attentive” at the time of the crash.21
We also conducted a more detailed analysis of inattentive drivers. As
figure 5 shows, overall, more drivers between ages 16 and 44 were
involved in inattentive-type crashes than drivers aged 45 and above. More
drivers aged 16 to 20 were inattentive than any other age group.

Figure 5: Inattentive Drivers Involved in Crashes by Age, 1997–2001




Note: This includes only those drivers involved in crashes where at least one passenger vehicle had
to be towed away.




21
 About 6 million were identified as “unknown” or “no driver present.”




Page 15                                                    GAO-03-436 Traffic Crash Causation
We also analyzed NHTSA’s databases to determine specific sources of
distraction. We found that some outside person, object, or event was
identified as contributing to 27 percent of the distractions. Other common
sources of distractions included another occupant in the vehicle, followed
by adjusting a radio, cassette, or CD.

A recent study by the AAA Foundation for Traffic Safety analyzed 1995
through 1999 NHTSA crash data on driver attention status and sources of
distraction and found that 8 percent of drivers were identified as
distracted, 5 percent as “looked but did not see,” and 2 percent as sleepy
or asleep, while 49 percent of the drivers were identified as attentive at the
time of the crash.22 The remaining 36 percent were either unknown or had
no driver present. Without the unknowns, the percentage of drivers
identified as distracted increases to 13 percent. The study also identified
specific sources of distraction. Some external person, object, or event
caused almost 30 percent of such distractions.

Drowsiness and fatigue are also aspects of inattention and can contribute
to crashes. Drowsiness is a basic physiological state, brought about by the
restriction or interruption of sleep. It also results from natural changes in
the body’s level of alertness during each 24-hour sleep-wake cycle.
According to the National Sleep Foundation, our internal body clocks
program us to be sleepy twice a day: first during the early morning hours
between midnight and dawn, and again between 1:00 p.m. and 4:00 p.m.
For the driver, the main effect of drowsiness or fatigue is a progressive
withdrawal of attention from the road and traffic demands, leading to
impaired performance behind the wheel. Drivers can become so fatigued
that they are slow to perceive risky situations and are unable to respond
quickly enough to avoid a crash. Fatigue can also arise because of
medication or illness.

According to an official from the National Sleep Foundation, studies have
shown that sleep-deprived individuals are less likely to be able to
concentrate on the task at hand. In addition, as people get tired they
engage in behaviors that lead to other distractions, such as smoking,
drinking or eating, turning up the radio, or employing other “tricks” to try
to stay awake. The official also told us that the foundation’s national polls


22
  Jane C. Stutts, Donald W. Reinfurt, Loren Staplin, and Eric A. Rodgman, The Role of
Driver Distraction in Traffic Crashes (Washington, D.C.: University of North Carolina for
the AAA Foundation for Traffic Safety, May 2001). This study examined drivers involved in
crashes where at least one vehicle had to be towed away.




Page 16                                             GAO-03-436 Traffic Crash Causation
                         and international studies support the perspective that driver fatigue is a
                         much larger problem than what the federal statistics show. Recently, the
                         National Sleep Foundation conducted a telephone survey and found that
                         about 51 percent of the respondents reported that they had driven a car or
                         another vehicle while feeling drowsy, and about 17 percent had dozed off
                         while driving within the past year.23 The study found that male respondents
                         were more likely than female respondents to say they had driven while
                         feeling drowsy. In addition, respondents with children and respondents
                         aged 18 to 29 were at the highest risk for driving while feeling drowsy. The
                         study also found that older respondents, 65 and over, are less likely to
                         drive drowsy or to fall asleep at the wheel.

Driver Decision Errors   Driver decision errors involve misjudgments made while driving. These
                         include improperly judging stopping distances, improperly judging
                         distances of cars traveling behind the vehicle, and other misjudgments of
                         distance between cars that result in a crash. Decision errors also include
                         crashes that result from traveling the wrong way on a one-way street. A
                         driver decision error differs from an error that may have resulted from
                         inattention or distraction because the driver sees a hazard, such as an
                         oncoming car making a left-hand turn, but makes the wrong decision
                         concerning the proper action to take.

                         A recent study by Veridian Engineering examined unsafe driving acts in
                         severe crashes in four sites across the United States to determine the
                         specific driver behaviors and unsafe driving acts that lead to crashes,
                         along with the situational, driver, and vehicle characteristics associated
                         with these behaviors.24 According to the study, in 717 of the 723 crashes
                         analyzed (99 percent), a driver behavioral error caused or contributed to
                         the crash. Of the 1,284 drivers involved in these crashes, 732 drivers
                         (57 percent) contributed in some way to the cause of their crashes.

Age                      There is a strong relationship between a driver’s age and the likelihood of
                         being involved in a crash. While age, in itself, would not be the cause of


                         23
                          The National Sleep Foundation commissioned WB&A Market Research to conduct the
                         2002 “Sleep in America” telephone poll of 1,010 adults at least 18 years old between
                         October 1 and December 10, 2001. The margin of error is plus or minus 3.1 percent.
                         24
                           D. L. Hendricks, M. Freedman, P.L. Zador, and J.C. Fell, The Relative Frequency of Unsafe
                         Driving Acts in Serious Traffic Crashes (Washington, D.C.: Veridian Engineering, Westat,
                         Inc., and Star Mountain, Inc., January 2001). A sample of 723 crashes involving 1,284 drivers
                         was investigated at four different sites in the country between April 1, 1996, and April 30,
                         1997.




                         Page 17                                               GAO-03-436 Traffic Crash Causation
the crash, some of the characteristics displayed at various ages can lead to
a higher probability of being involved in traffic crashes.

Our analysis of NHTSA’s databases found that younger and older drivers
become involved in a greater number of crashes, especially fatal crashes,
than do other age groups. Figure 6 shows that drivers aged 16 through 20
and those aged 75 or more have a greater chance of being involved in fatal
crashes per vehicle mile traveled (VMT) than do other age groups.25

Figure 6: Number and Rate of Driver Involvement in Fatal Crashes by Age, 1997–
2001




25
  For this VMT analysis, we used data from 2001 National Household Travel Survey. The
National Household Travel Survey consists of household-based travel surveys conducted
every 5 years by DOT. Survey data are collected from a sample of U.S. households and
expanded to provide national estimates of trips and miles by travel mode, purpose, and a
host of other characteristics. The survey collects information on daily, local trips and on
long-distance travel in the United States.




Page 18                                                GAO-03-436 Traffic Crash Causation
According to the Insurance Institute for Highway Safety, teenagers’ crash
rates are disproportionately high mainly because of the drivers’ youth
combined with driving inexperience. A recent study by the Insurance
Institute for Highway Safety showed that the age factor plays out in a more
risky driving style among adolescents.26 The study, which reviewed and
summarized other research on the risks associated with younger drivers,
found that increased crash risk comes immediately on licensure and drops
very rapidly in the first few months. Compared with older drivers, this
study concluded that young people are more likely to drive at excessive
speeds, follow too closely, violate traffic signs and signals, overtake other
vehicles in a risky manner, allow too little time to merge, and fail to yield
to pedestrians. Risky driving leads young people into hazardous situations,
and inexperience makes it more difficult to cope with such situations. The
researchers also found that driving at night is associated with an increased
risk of serious crashes for young drivers. The driving task is more difficult
for young drivers when it’s dark, and the risky driving that involves
younger drivers, generally associated with recreational activities, is more
likely to occur at night. Fatigue and alcohol are also more likely to
contribute to younger drivers’ crashes during nighttime hours. The study
also found that there is a heightened crash risk when teenage drivers have
passengers in their vehicles. The study found that this increased risk is
present only for teenage drivers, and it increases incrementally with each
additional passenger.

Older drivers are also at increased risk, because the elderly have higher
rates of fatal crashes per vehicle mile traveled than all but the youngest
drivers. According to a recent study by the Insurance Institute for Highway
Safety, this is largely attributable to their increased fragility.27 In the study,
fragility started at age 60 to 64 and continued to rise with advancing age. In
addition, a recent study by Dr. Leonard Evans found that given similar
crash severity, older drivers are more likely to sustain fatal injuries than
younger drivers.28 The author suggested that if populations of 70-year-old



26
  A.F. Williams and S.A. Ferguson for the Insurance Institute for Highway Safety, “Rationale
for Graduated Licensing and the Risks It Should Address,” Injury Prevention, vol. 8 (2002),
pp. 9–16.
27
  Guohua Li, Elisa R. Braver, and Li-Hui Chen, Exploring the High Driver Death Rates per
Vehicle-Mile of Travel in Older Drivers: Fragility versus Excessive Crash Involvement
(Arlington, VA: Insurance Institute for Highway Safety, August 2001).
28
 Leonard Evans, “Age and Fatality Risk from Similar Severity Impacts,” Journal of Traffic
Medicine, vol. 29, 2001, pp. 10–19.




Page 19                                               GAO-03-436 Traffic Crash Causation
                       males and 20-year-old males were subjected to the identical mixes of blunt
                       trauma, the population of older males would sustain over two times more
                       fatalities. A similar comparison of female populations would yield almost
                       two times more fatalities for older females. In addition, a literature review
                       conducted by the University of Michigan Transportation Research Institute
                       found that older drivers are more likely to suffer from medical disabilities
                       that could impair their driving, and they may use medications that could
                       affect their driving performance.29 The study also found that with
                       increasing age, most drivers experience some loss of visual perception and
                       decreased cognitive and psychomotor functions. For example, a 1988 AAA
                       Traffic Safety Foundation study tested a small group of volunteers and
                       found that older adults with less joint flexibility exhibited poorer driving
                       ability than those with wider ranges of motion.30 In addition, according to
                       the FHWA Director of the Office of Safety Programs, frailty is not the sole
                       factor in older driver fatality rates, noting that drivers 85 and older have
                       more than twice the overall crash rate of middle-aged drivers aged 40
                       through 44.


Roadway Environment    The roadway environment is generally cited as the second most prevalent
Contributes to Motor   factor contributing to crashes by data, experts, and studies. It can be
Vehicle Crashes        defined as those factors external to the driver and the vehicle that increase
                       the risk of a crash. Roadway environment factors that contribute to, or are
                       associated with, crashes include the design of the roadway (for example,
                       medians, narrow lanes, the lack of shoulders, curves, access points, or
                       intersections); roadside hazards (for example, poles, trees, or
                       embankments adjacent to the road); and the roadway conditions (for
                       example, rain, ice, snow, or fog).

Roadway Design         The principal guidance on roadway design is the American Association of
                       State Highway and Transportation Officials’ (AASHTO) Policy on
                       Geometric Design of Highways and Streets. This guidance provides
                       recommendations on constructing the nation’s roadways, including such
                       features as the sharpness of curves, the slope of roadways, the width of



                       29
                        David W. Eby, Deborah A. Trombley, Lisa J. Molnar, and Jean T. Shope, The Assessment
                       of Older Drivers’ Capabilities: A Review of the Literature (Ann Arbor, MI: University of
                       Michigan Transportation Research Institute, August 1998).
                       30
                        Kenard McPherson, Jeffrey Michael, Andrew Ostrow, and Peter Shaffron, Physical
                       Fitness and the Aging Driver, Phase I (Washington, D.C.: AAA Foundation for Traffic
                       Safety, 1988).




                       Page 20                                             GAO-03-436 Traffic Crash Causation
lanes, and the design of medians and barriers. In general, different
functional road systems are constructed for specific purposes. For
example, Interstate highways are intended for high mobility and therefore
have limited access points, while local roads are designed for increased
access, which can limit mobility. Design principles generally suggest that
as average daily traffic increases, additional design elements should be
adopted that increase safety, including wider lanes, paved shoulders, and
clear zones (areas free of roadside hazards next to the roadway).

Based on FHWA’s data, we found that fatal crashes were more frequent on
rural roads than on urban roads.31 In 2001, rural roads handled only about
40 percent of all vehicle miles traveled, yet more than 60 percent of all
fatalities occurred on these roads. Figure 7 shows that fatality rates are
higher on rural roads in comparison with urban roads, regardless of the
road type.




31
 The term “urban” is used to denote the federal-aid legislation definition of an area. Such
areas include, at a minimum, a census place with an urban population of 5,000 to 49,999, or
a designated urbanized area with a population of 50,000 or more. Rural areas are those
areas outside urban areas.




Page 21                                              GAO-03-436 Traffic Crash Causation
    Figure 7: Fatality Rates by Type of Road System, 2001




    Note: The urban Interstate fatality rate also includes fatalities from other urban freeways
    and expressways.


    A recent FHWA study developed relationships between roadway features
    and crash rates on two-lane rural highways.32 For this study, FHWA
    developed predictive models to estimate the safety impacts of roadway
    design features. Studies have found that the following roadway design
    features can affect crash rates. Appendix III contains additional
    information on roadway design features.

•   Medians — Medians (that is, the physical separations between opposite
    lanes of traffic) provide a recovery area for out-of-control vehicles and
    reduce head-on crashes by separating traffic driving in opposite directions.



    32
     D.W. Harwood, F.M. Council, E. Hauer, W.E. Hughes, and A. Vogt, Prediction of the
    Expected Safety Performance of Rural Two-Lane Highways, FHWA-RD-99-207 (December
    2000).




    Page 22                                                GAO-03-436 Traffic Crash Causation
•   Lane width — Wider lanes may reduce crashes by allowing for greater
    separation between vehicles traveling in adjacent lanes as well as
    providing additional space to recover from near-crash situations.

•   Shoulders — Wide roadway shoulders that are paved provide an
    opportunity for drivers to recover from errors that cause a vehicle to stray
    out of a lane.

•   Curves — Curves have been shown to contribute to crashes, whether
    horizontal curves (left or right) or vertical curves (up and down). Crash
    rates on curves are associated with their design features (including degree,
    length, and angle) and cross-sectional curve elements (lane width,
    shoulder size and type, and median characteristics).

•   Access points — As the number of access points, or locations where
    vehicles can gain entry to the roadway, increases, the more likely it is that
    a traffic crash will occur.

•   Intersections — Intersections, or at-grade locations where vehicles may
    transfer between roads, are among the most complex roadway designs a
    driver encounters. This is the result of increased points of conflict
    between vehicles, and between vehicles and pedestrians.

    FHWA’s Chief Highway Safety Engineer told us that it is important that a
    roadway be designed to allow a driver the time and space to make and
    recover from various errors without crashing. For example, two-lane rural
    roads are often characterized by sharp horizontal and vertical curves,
    narrow lanes, no shoulders or narrow ones, and roadside hazards such as
    utility poles or trees adjacent to the road. These design elements can be
    associated with higher fatality rates. This contrasts with the multilane
    highways, which generally have gradual horizontal and vertical curves,
    wider lanes and shoulders, and wide, clear zones adjacent to the road.

    FHWA’s Director of Office of Safety Research and Development pointed
    out that there are some data limitations associated with crashes and
    roadway design. For example, the Director noted that NHTSA’s crash
    databases contain very limited data on roadway design features at the
    crash location or immediately preceding the crash location. Accordingly,
    detailed analysis comparable to what is possible for the driver is not
    possible for the roadway. The Director also stated that efforts are
    underway to provide the means to more precisely locate the point of a
    crash and to relate that location to detailed roadway and roadside
    information databases.



    Page 23                                      GAO-03-436 Traffic Crash Causation
Roadside Hazards     Roadside hazards are physical features that a vehicle can crash into if it
                     leaves the roadway. Each year, about 14,000 persons are killed and almost
                     1 million persons are injured when vehicles run off the road and crash.
                     Many of these deaths and injuries result from crashes into poles and trees,
                     which are often located close to the edge of the roadway.

                     Our analysis of NHTSA’s data found that 16 percent of all crashes from
                     1997 through 2001 involved striking a roadway object as the first
                     property-damaging or injury-producing event in the crash. In addition, we
                     found that that in these crashes, posts or poles were the most common
                     fixed objects for a vehicle to hit after leaving the roadway (about 20
                     percent), followed by ditches (14 percent), trees (14 percent), and
                     guardrails (11 percent).

                     The Washington State Transportation Center conducted a study examining
                     roadside crashes on a single section of roadway.33 Models were created to
                     predict the frequency and severity of run-off-the-road crashes related to a
                     variety of roadway environmental factors. The study found, for example,
                     that both a decreased distance from the outside shoulder edge to roadside
                     objects and an increased number of trees near the roadway increased the
                     likelihood of a crash. Overall, the study supported the enlargement of
                     roadside recovery space to decrease the occurrence and severity of run-
                     off-the-road crashes.

                     The chairperson of AASHTO’s Task Force on Roadside Safety addressed
                     the importance of roadside hazards. The AASHTO official said that, in
                     order of preference, the four methods for addressing roadside hazards are
                     to (1) remove it, (2) relocate it, (3) redesign it, and (4) shield the roadside
                     hazards (for example, a guardrail or impact barrier).

Roadway Conditions   Roadway conditions can contribute to crashes through both road surface
                     conditions and reduced visibility. Surface conditions that can impair a
                     driver’s ability to control the vehicle include standing water, snow, ice,
                     and oil, in addition to such road surface features as holes, ruts, paved edge
                     drop-offs, and worn surfaces. Crashes can also result when visibility is
                     somehow reduced, preventing a driver from receiving the proper visual




                     33
                      Jinsun Lee and Fred Mannering, Analysis of Roadside Crash Frequency and Severity
                     and Roadside Safety Management, Washington State Transportation Center (December
                     1999).




                     Page 24                                          GAO-03-436 Traffic Crash Causation
driving cues. Reduced visibility can occur because of weather-related
events or the presence or absence of natural or artificial lighting.

Surface conditions. Common road surface conditions that can create
slippery roads are rain, snow, and ice. Slippery road conditions lead to a
loss of friction between a vehicle’s tires and the roadway. This loss of
friction may lead to the reduced controllability of the vehicle, ultimately
resulting in a crash.

Our analysis of NHTSA’s data from 1997 through 2001 found that about 23
percent of crashes occurred when road surface conditions were either
wet, snowy, slushy, or icy. In addition, a recent study by Iowa State’s
Center for Transportation Research and Education examined the
weather’s impacts on safety.34 The researchers examined the impact of
more severe winter storms on volume, safety, and speed characteristics on
seven segments of Interstate highways in Iowa. Their analysis of 54 storm
events concluded that crash rates increased by over 1,000 percent during
winter storm events with high snowfall rates.

Reduced visibility. Reduced visibility can occur during nighttime hours
(including dawn and dusk) and during weather-related events, such as fog,
rain, or snow. Reduced visibility can decrease a driver’s ability to receive
the proper visual cues to successfully navigate the road.

Our analysis of NHTSA’s data found that overall, while 15 percent of all
crashes took place under limited light conditions, about 34 percent of all
traffic fatalities occurred at that time. Although other factors are involved
during nighttime crashes, such as alcohol or fatigue, the reduction of
visual cues for the driver also appears to play a role.

The primary purpose of roadway lighting is to provide increased visibility
of the roadway and its immediate environment, to allow a person to drive
more efficiently and safely. An FHWA study examined the impact of
lighting options on urban freeways in Minnesota.35 The study used data on
crashes, roadways, and traffic volume to compare the safety of



34
 Keith K. Knapp, Dennis Kroeger, and Karen Giese, The Mobility and Safety Impacts of
Winter Storm Events in a Freeway Environment Final Report, Iowa State Center for
Transportation Research and Education (February 2000).
35
 Federal Highway Administration, Comparison of the Safety of Lighting Options on
Urban Freeways, FHWA Public Roads On-Line (Autumn 1994).




Page 25                                            GAO-03-436 Traffic Crash Causation
                             continuously lighted urban freeways with that of urban freeways having
                             interchange lighting only. Using data from between 1985 and 1990, the
                             study determined that 12 percent more crashes occur on sections with
                             interchange-only lighting than on road sections with continuous lighting,
                             assuming all other factors remain the same. The study concluded that
                             there was a positive relationship between urban freeway lighting and
                             highway safety.

                             Weather-related phenomena can also inhibit driver visibility. While fog
                             crashes are proportionally small compared with all other crashes, they can
                             involve numerous vehicles in a chain-reaction pileup. A recent example of
                             this occurred in Wisconsin in October 2002, where a fog-related crash
                             involving 51 vehicles resulted in 10 deaths. The National Transportation
                             Safety Board has concluded that major fog-related incidents generally
                             occur because drivers have not maintained uniform reduced speeds during
                             times of limited visibility.

                             According to NHTSA’s Director of the Office of Human-Centered
                             Research, the significance of adverse weather, including both slippery
                             roads and reductions in driver visibility, is not fully understood because
                             there are no measurements (for example, vehicle miles traveled under
                             adverse weather conditions) available to make comparisons between
                             crash rates under various conditions. A researcher at the University of
                             Michigan’s Transportation Research Institute said that pedestrian-related
                             crashes are particularly sensitive to light conditions. The researcher
                             pointed out that, unlike vehicles and roads that may have lighting or
                             reflective markings, pedestrians are generally not highly visible and are
                             more likely to be involved in crashes during nighttime hours.


Vehicle Factors Contribute   Vehicle factors can contribute to crashes through vehicle-related failures
to Motor Vehicle Crashes     and vehicle design characteristics (attributes that may increase the
                             likelihood of being involved in certain types of crashes). While such recent
                             events as the number of crashes involving tire separations have
                             highlighted the importance of vehicle factors, it is generally shown by data
                             and studies and believed by experts that vehicle factors contribute less
                             often to crashes than do human or roadway environment factors.

Vehicle-Related Failures     Two types of vehicle-related failures can contribute to traffic crashes:
                             equipment-related and maintenance-related. Equipment-related failures
                             include both original manufacturer and aftermarket-installed vehicle
                             equipment that function improperly. If not corrected, some equipment-
                             related failures might lead to the loss of a vehicle’s handling capabilities,


                             Page 26                                       GAO-03-436 Traffic Crash Causation
                 resulting in traffic crashes. The widely publicized tire separations are a
                 recent example of an equipment-related failure. Equipment-related failures
                 can be identified by the manufacturer or by NHTSA, and may result in a
                 recall. In 2002, NHTSA reported 413 recalls involving over 18 million
                 vehicles, over 1 million pieces of equipment, about 675,000 tires, and over
                 1 million child safety seats. NHTSA’s Director of the Office of Defects
                 Investigations told us that its investigations have identified 143 fatalities
                 associated with recalls from 1990 through 2000. Maintenance-related
                 failures result from an operator’s improper maintenance of vehicle
                 components, which may impair the function of the vehicle’s equipment.
                 Examples of maintenance-related failures include inadequate tire tread
                 depth, worn brakes, unchecked or unchanged vehicle fluids, and
                 underinflated tires.

                 Our analysis of NHTSA’s data found that from 1997 through 2001, there
                 were about 778,000 crashes in which police identified that a specific
                 vehicle-related failure might have contributed to the crash. Where these
                 failures were identified, brake systems and tires were identified most
                 frequently, at 29 percent and 27 percent, respectively. Data is not collected
                 by NHTSA in a manner that provides information on whether these
                 crashes were caused by equipment or maintenance-related failures.

                 One vehicle factor that NHTSA believes may contribute to crashes is
                 underinflated tires. In 2001, NHTSA conducted a study that found that 27
                 percent of passenger cars and 33 percent of light trucks were being driven
                 with one or more underinflated tires. To reduce this problem, Congress
                 passed the Transportation Recall Enhancement, Accountability, and
                 Documentation Act of 2000 (P.L. 106-414), which will require motor
                 vehicles to be equipped with a tire-pressure monitoring system to warn the
                 driver if a tire is significantly underinflated. In May 2002, NHTSA issued
                 part one of a two-part final rule requiring this system. It requires that
                 between November 1, 2003, and October 31, 2006, auto manufacturers
                 phase in one of two different tire-monitoring systems. The second rule,
                 which has yet to be finalized, is scheduled to be issued March 1, 2005.

                 Several officials told us that vehicle-related failures and their effect on
                 crashes are difficult to quantify. For example, NHTSA’s Chief of
                 Information Services stated that the central problem with identifying
                 vehicle factors is that police officers are not necessarily qualified to
                 identify vehicle defects.

Vehicle Design   The design of a vehicle has been shown to affect handling in particular
                 types of maneuvers. For example, high-performance sports cars have very


                 Page 27                                       GAO-03-436 Traffic Crash Causation
different handling characteristics from those of sport utility vehicles
(SUV). Recent changes in the composition of the nation’s vehicle fleet, in
part attributable to the purchase of many SUVs, have resulted in an overall
shift toward vehicles with a higher center of gravity (more top-heavy),
which can roll over more easily than some other vehicles. Rollover crashes
are particularly serious because they are more likely to result in fatalities.
NHTSA has developed rollover ratings for vehicles by calculating their
static stability. This factor is a static metric that is determined by dividing
a vehicle’s track width, or distance between wheels from side to side, by
twice the height of its center of gravity.

As shown in figure 8, our analysis of NHTSA’s 2001 data showed that vans
were the least likely to be involved in a crash, with about 432 crashes per
100 million vehicle miles traveled (VMT).36 Passenger cars were the most
likely to be involved in a crash, with a rate of 655 crashes per 100 million
VMT. The figure also shows that both vans and SUVs had the lowest fatal
crash rate, at 1.9 and 2.3 fatal crashes per 100 million VMT, respectively.




36
 For this VMT analysis we used data from the 2001 National Household Travel Survey.




Page 28                                            GAO-03-436 Traffic Crash Causation
Figure 8: Vehicle Crash Rates, 2001




In 2001, rollover crashes killed 10,118 occupants in passenger cars, pickup
trucks, SUVs, and vans. This represents almost one-third of the year’s
31,875 occupant deaths in these types of vehicles. Figure 9 shows the
percentage of rollover occurrence by vehicle type in 2001. Passenger cars
were the vehicle type least likely to roll over in a crash; passenger cars
rolled over in about 2 percent of all crashes, and rolled over nearly 16
percent of the time in fatal crashes. In comparison, our analysis shows that
SUVs were over three times more likely to roll over in a crash than were
passenger cars; that is, occurring in almost 6 percent of all crashes. The
proportion of SUVs that rolled over in fatal crashes was over twice as high
when compared with passenger cars. In 2001, SUVs rolled over in fatal
crashes over 35 percent of the time.




Page 29                                     GAO-03-436 Traffic Crash Causation
Figure 9: Passenger Vehicle Rollovers, 2001




The National Transportation Safety Board (NTSB) recently examined
rollovers in 15-passenger vans from 1991 through 2000.37 The NTSB found
that 15-passenger vans with 10 to 15 passengers had a rollover rate about
three times greater than that of vans seating 5 or fewer passengers. In
addition, NTSB found that the 15-passenger vans carrying 10 to 15
passengers rolled over in 96 of the 113 single-vehicle crashes (85 percent).
However, they also found that the vans rolled over only 28 percent of the
time, or 69 times out of the 244 single-vehicle crashes, when there were
fewer than 5 occupants in the van. Additional analysis showed that higher
speeds were also strongly correlated with a greater chance of rollovers.
NTSB recommended that 15-passenger vans be rated by NHTSA for
rollover propensity. Although NHTSA has established a rollover resistance



37
 National Transportation Safety Board, Evaluation of the Rollover Propensity of 15-
Passenger Vans, NTSB SR-02/03 (October 2002).




Page 30                                             GAO-03-436 Traffic Crash Causation
rating system and is currently developing dynamic rollover tests, 15-
passenger vans will not be evaluated for rollover propensity because they
exceed the weight criteria for the testing program.

A study by the Insurance Institute for Highway Safety examined single-
vehicle rollover crashes.38 The study concluded that the combined rollover
crash rate for pickup trucks and SUVs was more than twice the rate for
passenger cars. The higher rollover rate for pickup trucks and SUVs was
present even when taking into consideration a variety of crash
circumstances, including location, roadway alignment, and the driver’s
age. The study concluded that both pickup trucks and SUVs are more
prone to rollover crashes than are passenger cars.

A recent NHTSA study addressed rollovers from 1991 through 2000.39 One
of its findings was that of all vehicle types considered in the study, SUVs
are the only type in which the number of occupant fatalities in rollover
crashes exceeds the number of occupant fatalities in nonrollover crashes;
in 2000, nearly two-thirds of SUVs’ occupant fatalities occurred in rollover
crashes. One of the report’s conclusions was that, despite declines in
passenger car occupant fatalities, the increasing influence of light truck
fatal crashes in general, and rollover crashes in particular, is instrumental
in maintaining the level of traffic crash fatalities. NHTSA’s Division Chief
of Math Analysis stated that reducing rollovers is one of the NHTSA
Administrator’s top five priorities.

In commenting on a draft of this report, NHTSA provided an analysis
comparing the crash rates for both passenger cars and light trucks using
VMT based on FHWA’s Highway Statistics Series.40 The analysis indicates
that passenger cars had a lower fatal crash rate at 1.73 per 100 million
VMT, as compared with a rate of 2.13 for light trucks. With regard to the


38
  Charles Farmer and Adrian Lund, “Rollover Risk of Cars and Light Trucks after
Accounting for Driver and Environmental Factors,” Accident Analysis and Prevention,
vol. 34 (2002), pp. 163–73. The study examined all single-vehicle fatal crashes for 4 years,
along with single-vehicle injury crashes involving rollovers from three states by vehicle
type for 4 years. The study used vehicle registration as a means to make comparisons
among vehicle types.
39
 William Deutermann, Characteristics of Fatal Rollover Crashes, DOT HS 809 438 (April
2002).
40
 This VMT analysis used the FHWA’s Highway Statistics Series. FHWA obtains its data on
vehicle miles traveled by counting the number and types of vehicles passing particular
points around the country.




Page 31                                                GAO-03-436 Traffic Crash Causation
                        vehicle involvement rate in all crashes, NHTSA’s analysis shows that
                        passenger cars had a rate of 423 crashes per 100 million VMT, which is
                        slightly higher than that for the light trucks (401 crashes per 100 million
                        VMT).

                        In February 2003, the Alliance of Automobile Manufacturers, a trade group
                        that represents the three major U.S. automobile manufacturers and a
                        number of foreign manufacturers, published analyses examining occupant
                        fatality rates by vehicle type. One analysis used registered vehicles as a
                        method to compare fatality rates between vehicle types. Its results
                        indicate that in 2001, SUVs had a slightly higher occupant fatality rate than
                        had passenger cars—16.25 and 15.70 per 100,000 registered vehicles,
                        respectively. The alliance points out, however, that 72 percent of people
                        killed in SUV rollover crashes were not wearing safety belts, which can
                        reduce a driver’s risk of fatal injury in a rollover by 80 percent. They
                        further stated that in 2000, 35 percent of SUV single-vehicle rollover
                        fatalities were alcohol-related.


                        Various modal agencies within the Department of Transportation have
Federal Research        research projects underway and planned that address aspects of crash
Directed at Better      causes. For example, the Federal Motor Carrier Safety Administration and
                        NHTSA are conducting a study on the causes and contributing factors to
Understanding of        large truck crashes. NHTSA is also funding the 100-Car Naturalistic
Factors That            Driving Study, which involves collecting data about crashes and near
                        misses from 100 vehicles equipped with sensors. Further, NHTSA is
Contribute to Crashes   funding a project called the Drive Atlanta Study that involves collecting
                        data from 1,100 vehicles equipped with data recorders. In addition to
                        possible follow-on research on the above projects, planned research
                        includes a Transportation Research Board proposal for a 6-year program
                        that would, among other things, involve installing sensors and other data
                        collection devices on over 5,000 vehicles.


Large Truck Crash       In 1999, Congress established the Federal Motor Carrier Safety
Causation Study         Administration (FMCSA) within DOT and mandated that it study the
                        causes of and contributing factors in large truck crashes. In 2001, large
                        truck crashes resulted in about 5,000 fatalities and 131,000 injuries.
                        FMCSA partnered with NHTSA to implement the 4-year, $18 million Large
                        Truck Crash Causation Study. The study’s goal is to develop a greater
                        understanding of the factors leading to large truck crashes, so that cost-
                        effective countermeasures can be developed to decrease the number and
                        severity of these crashes.


                        Page 32                                       GAO-03-436 Traffic Crash Causation
                             To conduct this study, FMCSA and NHTSA built on the existing crash
                             investigation system that NHTSA had established to collect data for the
                             Crashworthiness Data System database. For this effort, researchers at 24
                             locations collect information on a sample of large truck crashes by visiting
                             the crash sites shortly after they occur and completing a response protocol
                             that was developed for this project. NHTSA’s Director of the National
                             Center on Statistics and Analysis told us that the most informative crash
                             causation data is often collected at the site of the crash while the vehicles
                             and participants are still present.

                             Cooperative agreements were established between the police, FMCSA,
                             and NHTSA to use an established, on-scene investigative approach. These
                             cooperative agreements were based on previous agreements set up
                             between NHTSA and police for data collection for the CDS database, but
                             they were modified to accommodate the other parties involved and a
                             faster time frame for the crash investigations. A NHTSA official stated that
                             this multiagency partnering is important for the success of the study, and
                             that establishing rapid notification procedures requires the cooperation of
                             state and local police along with their police dispatch personnel.

                             The researchers expect to investigate at least 1,000 crashes by the end of
                             2003. FMCSA and NHTSA officials said that the results will yield findings
                             about critical pre-crash events, the reasons for these events, and relative
                             risks in truck crashes. They also said that this information should
                             significantly help to create proven countermeasures to decrease the
                             number and limit the severity of truck crashes.

                             As a follow-on to this study, NHTSA requested $10 million in its fiscal year
                             2004 budget to begin a National Motor Vehicle Crash Causation Survey.
                             This study would develop and conduct a nationally representative effort to
                             collect on-scene crash causation data. The Large Truck Crash Causation
                             Study would be used as the model for the proposed study. The on-scene
                             methodologies and procedures developed for the Large Truck Crash
                             Causation Study would also be applicable to this proposed effort. NHTSA
                             officials said that start-up costs and implementation timing would be
                             reduced by making use of the infrastructure in place for the truck study,
                             which is scheduled to complete data collection by the end of 2003.


One Hundred-Car              NHTSA is currently conducting the 100-Car Naturalistic Driving Study,
Naturalistic Driving Study   whose purpose is to help develop better crash-avoidance warning systems.
                             This 1-year, $3 million driving research study involves collecting data from
                             100 vehicles equipped with various sensors and cameras. NHTSA has


                             Page 33                                      GAO-03-436 Traffic Crash Causation
                      partnered with FHWA, Virginia, and the Virginia Polytechnic Institute and
                      State University (Virginia Tech) to fund the study. Virginia Tech is
                      responsible for conducting the study.

                      NHTSA has equipped 100 cars (80 individually owned and 20 leased) with
                      five video cameras and a variety of sensors to track proximity and
                      relationships to other vehicles and objects. In addition, the vehicles have
                      sensors that detect glare and whether the driver is using a cell phone in
                      the car. Volunteers will use the vehicles for their everyday driving in the
                      metropolitan Washington, D.C., area for the duration of the study, which
                      began in early 2003. The cameras and sensors are to provide data for
                      studying crashes as well as near misses. In the event of a crash, NHTSA
                      will send a team of researchers to the site to investigate.

                      NHTSA officials told us that they are considering a follow-on to this study,
                      if it is successful. An expanded version of the study could include a
                      representative sample of up to 10,000 equipped cars around the country.
                      The official said that after completion of the initial study, researchers
                      should have greater knowledge about which sensors and equipment
                      provided the most relevant information on contributing factors to motor
                      vehicle crashes, and would install only that equipment in the larger fleet of
                      vehicles. NHTSA told us that they might seek funding from auto
                      manufacturers and other entities to supplement their funding.


Drive Atlanta Study   Later this year, NHTSA will begin a 2-year, $3.1 million Drive Atlanta
                      Study, which involves installing data recorders in 1,100 vehicles to develop
                      information on situations and circumstances where excessive speed
                      contributes to crashes. Drive Atlanta is primarily funded by a $1.9 million
                      contract with NHTSA and $1.2 million from Safety Intelligence Systems,
                      Inc. FHWA is also contributing money to the study. The private company is
                      providing the development costs and is prototyping and testing the
                      MACBOX, the data recorder that will be used by the Georgia Institute of
                      Technology to conduct the study.

                      In this study, the data recorder information will be combined with three
                      other types of data. Data will be contributed by the Atlanta Traffic
                      Management Center on prevailing traffic conditions, the National Oceanic
                      and Atmospheric Administration on weather, and the Georgia Department
                      of Transportation on roadway characteristics. According to a program
                      official, this combination of data will enable the researchers to know when
                      and where the driving occurred, what were the posted speed limits along
                      the drivers’ routes, what were the roads’ characteristics, and numerous


                      Page 34                                      GAO-03-436 Traffic Crash Causation
                           other data. The researchers plan to create speed profiles for all of the
                           study’s participants at the conclusion of the study, to examine exactly how
                           speed is involved in crashes. NHTSA estimates that at least 100 crashes
                           will occur over the next 2 years involving these vehicles.


Future Strategic Highway   In the Transportation Equity Act for the 21st Century (P.L. 105-178),
Research Program           Congress requested that the Transportation Research Board conduct a
                           study to determine the goals, purposes, research agenda and projects,
                           administrative structure, and fiscal needs for a new strategic highway
                           research program. In response to this request, a committee of highway
                           industry leaders was formed to develop recommendations. The committee
                           engaged in an outreach process to gather input from the highway
                           community regarding strategic priorities and promising research
                           approaches. The committee’s report was published in October 2001 and
                           recommended a 6-year, $450 million to $500 million Future Strategic
                           Highway Research Program (F-SHRP) focused on the following areas: (1)
                           accelerating the renewal of America’s highways; (2) making a significant
                           improvement in highway safety; (3) providing a highway system with
                           reliable travel times; and (4) providing highway capacity in support of the
                           nation’s economic, environmental, and social goals. FHWA contributed
                           $1.5 million over fiscal years 2002 and 2003 toward the F-SHRP planning
                           activities.

                           The F-SHRP objective of “making a significant improvement in highway
                           safety” includes three major areas: (1) methodology development using
                           existing data, (2) large-scale research studies of multiple factors related to
                           the risk of collisions and casualties for high priority roadway safety issues,
                           and (3) analysis of the field data for countermeasure implications. A key
                           aspect of this project is the use of in-vehicle and roadside technologies to
                           gather data to examine crash rates and pre-crash conditions on a large
                           scale to perform risk analyses. The study recommended that $180 million
                           to $200 million be committed to this safety objective.

                           The F-SHRP safety plan includes using the data from NHTSA’s national
                           crash databases as well as other studies that have used instrumented
                           vehicles and roadside technologies. The F-SHRP study would involve
                           collecting data from 5,000 to 6,000 instrumented vehicles and roadside
                           technologies for over 2 to 3 years. According to the contractor who
                           developed the implementing plan for the F-SHRP safety goal, analysis of
                           the previous study data will enable the F-SHRP researchers to first test
                           risk measures and analysis methods before implementation of the F-SHRP
                           field study. The contractor said that NHTSA’s 100-Car Naturalistic Driving


                           Page 35                                      GAO-03-436 Traffic Crash Causation
                     Study and Drive Atlanta Study and FHWA’s Road Departure Study would
                     be good sources of the type of instrumented vehicle data the early
                     methodology projects need.41 The proposed F-SHRP instrumented vehicle
                     study would involve data collection for two high-priority highway safety
                     problems: run-off-the-road and intersection crashes. The fleet of
                     instrumented vehicles would be split between at least two geographic
                     areas, with volunteer drivers using the vehicles for their everyday driving.
                     The final phase of the research would be to use the results of the large-
                     scale instrumented vehicle study to identify appropriate countermeasure
                     improvements.


                     We provided copies of a draft of this report to the Department of
Agency Comments      Transportation for its review and comment. In discussing this report,
and Our Evaluation   NHTSA and FHWA officials provided technical clarification and
                     information, which we incorporated in the report as appropriate. In
                     addition, NHTSA provided information comparing light truck and
                     passenger car crash rates, which we also incorporated in the report.


                     As arranged with your offices, unless you publicly announce its contents
                     earlier, we plan no further distribution of this report until 30 days after the
                     date of this letter. At that time, we will send copies of this report to
                     cognizant congressional committees and to the Honorable Norman Y.
                     Mineta, Secretary of Transportation; the Honorable Dr. Jeffrey W. Runge,
                     Administrator of the National Highway Traffic Safety Administration; and
                     the Honorable Mary E. Peters, Administrator of the Federal Highway
                     Administration. We will also make copies available to others upon request.
                     In addition, the report will be available at no charge on the GAO Web site
                     at http://www.gao.gov.




                     41
                       In the Road Departure Study, the University of Michigan Transportation Research
                     Institute will develop and test a new crash avoidance warning system in 11 passenger cars.
                     The system, designed to prevent road departure and run-off-the-road crashes, will alert the
                     driver when the vehicle begins to wander off the road or when the vehicle is traveling too
                     fast for an upcoming curve.




                     Page 36                                               GAO-03-436 Traffic Crash Causation
If you have questions about the report, please contact me at (202)
512-2834. Key contributors to this report were Michele Fejfar, Glenn C.
Fischer, Bonnie Pignatiello Leer, Sara Ann Moessbauer, Elsie Picyk,
Beverly Ross, and Glen Trochelman.




Peter Guerrero
Director, Physical Infrastructure Issues




Page 37                                     GAO-03-436 Traffic Crash Causation
                      Appendix I: Objectives, Scope, and
Appendix I: Objectives, Scope, and
                      Methodology



Methodology

                      To provide information on the factors that contribute to motor vehicle
                      crashes, we obtained and analyzed crash data from National Highway
                      Traffic Safety Administration (NHTSA) databases, obtained and reviewed
                      research studies on the topic, and interviewed a variety of experts and
                      federal officials. To identify major ongoing and planned Department of
                      Transportation (DOT) research into factors that cause crashes, we
                      obtained documents from and interviewed officials of NHTSA and the
                      Federal Highway Administration (FHWA).


                      For each factor contributing to traffic crashes, we obtained and analyzed
Analyzing NHTSA       data for calendar years 1997 through 2001 from NHTSA’s crash reporting
Data                  systems—the most recent 5-year period for which these data are available.
                      Our analysis involved the use of three of NHTSA’s databases: the Fatality
                      Analysis Reporting System, the General Estimates System, and the
                      Crashworthiness Data System. Each database contained different levels of
                      crash data.

                  •   Fatality Analysis Reporting System (FARS) – This database provides
                      information on all traffic-related fatalities. A crash must result in the death
                      of an occupant or nonmotorist within 30 days of the incident to be
                      included in this database. Each of the states provides the data to NHTSA in
                      a standardized format. The states generally obtain this information
                      through data from reports that police officials prepare at the scene of the
                      crash as well as state vehicle registration files, state driver licensing files,
                      state highway department data, death certificates, coroner or medical
                      examiner reports, hospital medical records, and emergency medical
                      service reports. NHTSA created the database to identify traffic safety
                      problems, develop and implement countermeasures, and evaluate vehicle
                      safety standards and highway safety programs. We used this database to
                      present overall information on traffic deaths as well as to provide an
                      understanding of crashes involving speed, alcohol, age, and vehicle design.
                      It should be noted that while fatality data is useful in understanding
                      crashes, other factors, in addition to those involved in causing the crash,
                      might have contributed to the fatality. This would include such factors as
                      whether safety belts or other occupant protection measures were used and
                      operated properly.

                  •   General Estimates System (GES) – This database is created from a
                      nationally representative sample of police accident reports completed for
                      crashes. Other criteria necessary for inclusion in the database are that the
                      crash must involve at least one motor vehicle traveling on a traffic way,
                      and that the crash must result in property damage, injury, or death. This
                      database was created to identify traffic safety problem areas, provide a


                      Page 38                                       GAO-03-436 Traffic Crash Causation
    Appendix I: Objectives, Scope, and
    Methodology




    basis for regulatory and consumer initiatives, and form the basis for cost
    and benefit analyses of traffic safety initiatives. This is NHTSA’s largest
    crash database, with information collected on over 50,000 randomly
    sampled police accident reports each year. We analyzed the GES data to
    provide information on speed, traffic control violations, roadside hazards,
    roadway conditions, and vehicle defects. In addition, for the analysis in
    which we compared fatalities with other types of crashes (reduced
    visibility, vehicle design, age), we combined FARS and GES data.

•   Crashworthiness Data System (CDS) – This database contains
    information from a detailed sample of about 4,000 minor, serious, and fatal
    crashes annually. The criterion necessary for inclusion in the database is
    that at least one passenger vehicle must be damaged severely enough to
    require towing from the crash site. Teams of trained crash investigators
    visit the crash site and collect data elements such as vehicle crash damage
    and interior vehicle locations that the occupants struck. The investigators
    also generally locate and interview crash victims and review medical
    records to determine the types of crash-related injuries. A goal of this
    database includes having the ability to examine the crashworthiness of
    vehicles; that is, how vehicles perform in crashes with respect to
    protecting their occupants. We used the CDS database to provide
    information on crashes involving driver inattention.

    In commenting on a draft of our report, NHTSA officials said that the
    FARS, GES, and CDS databases, although providing useful information,
    rely on data from police accident reports or on data collected days or
    weeks after the crash, making it difficult to obtain causation data.
    Therefore, NHTSA relies on the Indiana Tri-Level study data, which is
    almost a quarter of a century old. They noted that since the Tri-Level study
    was completed, cars, drivers, highways, technology, and lifestyles in the
    United States have changed dramatically. As previously discussed, NHTSA
    has proposed to develop and conduct a nationally representative survey to
    collect on-scene crash causation data—the National Motor Vehicle Crash
    Causation Survey. NHTSA officials indicated that these on-scene, real-time
    data are needed to best understand crash causation.

    In addition to using these three databases, for some analyses we also
    calculated frequency rates using vehicle miles traveled. We used vehicle
    miles traveled data from two different sources—the 2001 FHWA Highway
    Statistics Series data and the 2001 National Household Travel Survey. For
    example, we used FHWA’s vehicle miles traveled data in examining crash
    rates by road type. FHWA obtains its data on vehicle miles traveled by
    counting the number and types of vehicles passing particular points



    Page 39                                     GAO-03-436 Traffic Crash Causation
                      Appendix I: Objectives, Scope, and
                      Methodology




                      around the country. Because FHWA’s statistics do not include data on age
                      or gender, we used vehicle miles traveled from the 2001 National
                      Household Travel Survey for some analyses.42 This survey of about 26,000
                      households in the United States was conducted from March 2001 through
                      May 2002. It provides data on personal travel behavior at the national level
                      to use as a benchmark for a variety of applications. Although the overall
                      response rate for sampled households was low (41 percent), there are few
                      other sources for information on U.S. travel patterns. We used the most
                      recent available data, preliminary release (version 1), to get estimates of
                      annual vehicle miles traveled for our tables on rates of driver involvement
                      and types of vehicles involved in crashes.

                      We assessed the reliability of FARS, CDS, and GES by reviewing existing
                      information about the data and performing electronic tests of the data.
                      There are certain limitations associated with using these databases for our
                      analysis. For example, the source of the GES data is police accident
                      reports that are prepared at the scene of the crash. Although the GES has
                      procedures to ensure that data reflect information in the accident reports,
                      we did not verify the accuracy of the accident reports themselves. In
                      addition, since GES, CDS, and the National Household Travel Survey are
                      based on samples, any estimates derived from these databases are subject
                      to sampling errors. A sampling error indicates how closely the results of a
                      particular sample would be reproduced if a complete count of the
                      population were taken with the same measurement methods. The
                      estimated sampling errors (at the 95 percent confidence level) do not
                      exceed plus or minus 11 percentage points.


                      To identify recent studies on factors that contribute to motor vehicle
Identifying Studies   crashes, we conducted a literature search, explored the Transportation
                      Research Information System, and reviewed periodicals. This effort
                      resulted in numerous studies being identified on various aspects of the
                      motor vehicle crashes. We then, with input from a number of experts and
                      officials from NHTSA and FHWA, judgmentally selected studies that would
                      provide additional information on the particular factors being discussed.
                      For each of the selected studies that are used in this report, we determined
                      whether the study’s findings were generally reliable. To do so, we
                      evaluated the methodological soundness of the studies using common



                      42
                       2001 National Household Travel Survey User’s Guide, Version 1(Preliminary Release)
                      January 2003.




                      Page 40                                           GAO-03-436 Traffic Crash Causation
                        Appendix I: Objectives, Scope, and
                        Methodology




                        social science and statistical practices. For example, we examined each
                        study’s methodology, including its limitations, data sources, analyses, and
                        conclusions.


                        In conducting this review we interviewed a wide variety of federal officials
Interviewing Federal    and other experts. Within DOT, we interviewed officials from the Volpe
Officials and Experts   Center, the National Highway Traffic Safety Administration, and the
                        Federal Highway Administration. We also spoke with individuals affiliated
                        with academic institutions, including the University of North Carolina’s
                        Highway Safety Research Center, the University of Michigan’s
                        Transportation Research Institute, Northwestern University’s Center for
                        Public Safety, Texas A&M University’s Texas Transportation Institute, and
                        the Johns Hopkins School of Public Health. In addition, we interviewed
                        officials from the Insurance Institute for Highway Safety. We also spoke
                        with automobile industry representatives at the Alliance of Automobile
                        Manufacturers, a trade group that represents the three major U.S.
                        automobile manufacturers and a number of foreign manufacturers. We
                        spoke with officials from the Transportation Research Board, Advocates
                        for Highway and Auto Safety, AAA (formerly the American Automobile
                        Association), American Association of State Highway and Transportation
                        Officials (AASHTO), the National Sleep Foundation, the Midwest Research
                        Institute, and the Southern California Research Institute. In general, the
                        officials and experts provided information about major factors that
                        contribute to motor vehicle crashes and research on these factors.



                        To identify major ongoing and planned DOT research into factors that
Ongoing and Planned     contribute to motor vehicle crashes, we interviewed officials from NHTSA,
Transportation          FHWA, and the Transportation Research Board. These agencies have a
                        great deal of ongoing and planned research on a wide variety of motor
Research                vehicle safety issues, such as research to mitigate accident severity and
                        safety system issues. However, to respond to this objective, we selected
                        ongoing and planned studies that (1) represented major research studies,
                        (2) examined multiple factors contributing to crashes, (3) examined causal
                        factors rather than countermeasures, and (4) collected original data,
                        rather than analyzed existing data. We also obtained documents describing
                        the research projects and reviewed federal budgetary documents on the
                        projects.

                        We performed our review from July 2002 through February 2003 in
                        accordance with generally accepted government auditing standards.


                        Page 41                                     GAO-03-436 Traffic Crash Causation
                          Appendix II: Tri-Level Study of the Causes of
Appendix II: Tri-Level Study of the Causes of
                          Traffic Accidents



Traffic Accidents

                          Researchers at the Indiana University Bloomington’s Institute for Research
                          in Public Safety conducted the Tri-Level Study of the Causes of Traffic
                          Accidents from 1972 through 1977. The study investigated how frequently
                          various human, environmental, and vehicle factors were involved in traffic
                          crashes. According to NHTSA officials, the Tri-Level study has been the
                          only study in the past 30 years to collect on-scene crash causation data.
                          The study, conducted for NHTSA, incorporated 13,568 police-reported
                          crashes, including on-scene investigation of 2,258 crashes, and an in-depth
                          investigation of 420 crashes. The investigation teams assessed causal
                          factors as definite, probable, or possible. The in-depth team identified
                          human errors as definite or probable causes in 93 percent of the crashes,
                          environmental factors in 34 percent, and vehicle factors in 13 percent. In
                          20 percent of the crashes studied in depth, no definite cause could be
                          identified.


                          Indiana University conducted the study to satisfy a broad range of
Objectives, Scope,        NHTSA’s needs for data on traffic crash causation. Two of the main
and Methodology for       objectives for the research were to:
the Tri-Level Study   •   Identify those factors that are present and serve to initiate or influence the
                          sequence of events resulting in a motor vehicle crash.

                      •   Determine the relative frequency of these factors and their causal
                          contribution within a defined crash and within the driving population.

                          Researchers collected collision data on three levels (A, B, and C), each
                          providing an increasing amount of detail. Data collection for level A
                          involved examining police reports for 13,568 crashes and collecting other
                          baseline data, such as vehicle registration files, driver license files,
                          roadway inventories, and local surveys. For level B, teams of technicians
                          conducted on-site investigations of 2,258 crashes immediately following
                          their occurrence. For level C, a multidisciplinary team conducted
                          independent, in-depth investigations of 420 of the crashes. The crashes
                          investigated on-scene and in-depth were generally representative of all
                          police-reported crashes occurring in Monroe County, Indiana, during the
                          study period.

                          In the clinical assessments of crash causation in Monroe County, a traffic
                          crash was viewed as the last event in a chain of events and conditions that
                          preceded it. A crash cause was defined as an event or condition but for
                          which the crash would not have occurred. Emphasis was placed on events




                          Page 42                                         GAO-03-436 Traffic Crash Causation
                      Appendix II: Tri-Level Study of the Causes of
                      Traffic Accidents




                      and conditions that immediately preceded the crash because they may be
                      viewed as the final links of a casual chain that culminates in the crash.

                      According to the study, during in-depth investigations, the researchers
                      attempted to acquire as much relevant information as possible, and then
                      made clinical case-by-case determinations of the causal factors involved,
                      based on all of the information obtained. An assessment system permitted
                      each identified factor to be evaluated as definitely, probably, or possibly
                      involved as either a causal or severity-increasing factor. A causal factor
                      was defined as a factor necessary or sufficient for the occurrence of the
                      crash; had the factor not been present in the crash sequence, the crash
                      would not have occurred. A severity-increasing factor was defined as a
                      factor that was neither necessary nor sufficient for the occurrence of the
                      crash, but its removal from the crash sequence would have lessened the
                      speed of the initial impact. The causal assessment process for each crash
                      involved two major steps: first, identifying relevant deficiencies of drivers,
                      vehicles, and the driving environment that were present in the crash
                      sequence; and second, assessing the investigation team’s certainty that the
                      crash would not have occurred had each deficiency been corrected to its
                      minimally acceptable state.

                      In addition, data on Monroe County drivers, vehicles, roads, and crashes
                      were compared with available national data. It was found that for Monroe
                      County the severity distribution of reported crashes; the proportion of
                      crashes occurring on dry, wet, or snow- or ice-covered roads; the
                      proportion occurring in urban or rural areas; and the age distribution of
                      the vehicles were nearly the same as for the United States as a whole. The
                      most notable difference was that young drivers were overrepresented.
                      However, the effects of this overrepresentation on the overall causal
                      results were found to be minimal. Thus, it was found that while the results
                      from Monroe County, Indiana, do not represent the United States as a
                      whole in a statistical sense, they indicate factors that are likely to be
                      important on a national level and their relative involvement.


                      Human factors were the most frequently implicated of the three
Results of the Tri-   categories, and vehicle factors the least frequently implicated. As figure 10
Level Study           shows, the in-depth team concluded that human factors were definite
                      causal factors in 71 percent of the crashes; environmental factors in 13
                      percent; and vehicle factors in 4 percent. Similarly, the in-depth team
                      concluded that these same three categories were definite or probable
                      causal or severity-increasing factors in 93 percent, 34 percent, and 13
                      percent, respectively.


                      Page 43                                         GAO-03-436 Traffic Crash Causation
                Appendix II: Tri-Level Study of the Causes of
                Traffic Accidents




                Figure 10: Factors Contributing to Crashes Identified by the Tri-Level Study




                The on-site team concluded that human factors were definite causal
                factors in 64 percent of the crashes; environmental factors in 19 percent;
                and vehicle factors in 4 percent. The on-site team concluded that these
                same three categories were definite or probable causal or severity-
                increasing factors in 90 percent, 35 percent, and 9 percent, respectively.
                The in-depth team could not establish a definite cause for 20 percent of the
                crashes they investigated, while the on-site technicians could not establish
                a cause for 26 percent of the crashes. However, the on-site team identified
                one or more probable causes in nearly all the crashes. Also, more than one
                factor was implicated as a cause in many of the crashes.


Human Factors   The study categorizes human direct causes based on an information-
                processing model of the driver as vehicle controller. This model assumes
                that drivers are continuously engaged in perceiving and comprehending
                information, making decisions, and taking actions to achieve necessary
                control responses. The “perception” and “comprehension” categories were
                combined as “recognition errors” because of the difficulty in distinguishing



                Page 44                                          GAO-03-436 Traffic Crash Causation
                        Appendix II: Tri-Level Study of the Causes of
                        Traffic Accidents




                        errors in these functions through crash investigation. A “critical
                        nonperformance” category was added to reflect instances where a driver
                        ceases to perform as an information processor. A “noncrash” category was
                        included to accommodate any intentional crash involvements. Recognition
                        errors were cited as the most prevalent human causal factor, followed by
                        decision errors, performance errors, and critical nonperformance errors.

                        More specific human-direct-cause categories were grouped in the causal
                        hierarchy, under these major headings. With regard to specific human
                        errors, improper lookout was cited as the most prevalent error. Other
                        specific human errors cited included excessive speed, inattention,
                        improper evasive action, and internal distraction.

                        The researchers separately recorded human conditions and states that
                        impeded the ability of the driver to function as an information processor.
                        These factors, which included fatigue, driver experience, and alcohol
                        impairment, were viewed as potential “reasons behind the reasons.”
                        Alcohol impairment was cited as the most prevalent human condition,
                        followed by other drug impairment and fatigue.


Environmental Factors   The study categorized environmental factors as involving highway-related
                        factors, slick roads, or other ambience-related factors. Among these,
                        highway-related factors predominated; the in-depth team identified them
                        as definite causes in 7 percent of crashes. Slick roads were definite causes
                        in 4 percent of crashes, and other ambience-related factors in 2 percent.
                        More specific environmental causes were defined under these three broad
                        headings. The most commonly cited specific environmental factors were
                        view obstructions and slick roads.


Vehicle Factors         The study categorized vehicle factors according to major vehicle systems,
                        and then according to more specific categories. The most commonly cited
                        deficiency in these systems was with the brake system, followed by the
                        tires and wheels. The most commonly cited vehicle deficiency causal
                        factor was gross brake failure, followed by inadequate tread depth.




                        Page 45                                         GAO-03-436 Traffic Crash Causation
                         Appendix III: Roadway Design Features
Appendix III: Roadway Design Features


                         A number of roadway design studies and experts we spoke with addressed
                         how various aspects of roadway design might contribute to traffic crashes.
                         These included medians, lane widths, shoulders, curves, access points,
                         and intersections.


Medians                  Medians are physical separations between opposite lanes of traffic that
                         provide a recovery area for out-of-control vehicles. They also serve to
                         separate traffic driving in opposite directions, thereby minimizing their
                         interactions and likelihood of being involved in catastrophic head-on
                         crashes. Some considerations regarding medians include their presence or
                         absence (that is, divided vs. undivided roads), the width of the median,
                         and whether a barrier is placed in the median.

Presence or Absence of   An analysis of NHTSA’s databases showed that from 1997 through 2001, 44
Medians                  percent of all traffic fatalities occurred on undivided, rural, two-lane roads.
                         This represents 73 percent of all traffic fatalities in rural areas. In urban
                         areas, 35 percent of traffic fatalities occurred on two-lane undivided
                         roadways. In addition, a study conducted by the Kentucky Transportation
                         Center examined the impact of converting two-lane undivided rural roads
                         to four-lane divided roads at 25 locations.43 They found that, on average,
                         there was a reduction in crash rate after the road’s conversion from a
                         two-lane undivided rural road to a four-lane divided road.

Width of Medians         According to experts with whom we spoke, medians provide safety
                         benefits by allowing vehicles enough room to recover from various vehicle
                         or human factors that could contribute to a crash. A study published in the
                         Transportation Research Record used Highway Safety Information System
                         data from Illinois and Utah to assess the relationship between median
                         width and crash rates.44 The study was based on a total of 3,055.1 miles of
                         roadway, with speed limits of at least 35 miles per hour. The study
                         attempted to isolate only the median’s width as the predictive factor for
                         crash rates, but it acknowledged that there could be other elements
                         influencing the crash rates as well. Overall, the study concluded that crash
                         rates decrease with increasing median widths greater than 25 to 30 feet,




                         43
                          Kenneth Agent and Jerry Pigman, Safety Impacts of Rural Road Construction, Kentucky
                         Transportation Center KTC-01-01(February 2001).
                         44
                          M.W. Knuiman, F.M. Council, and D.W. Reinfurt, The Effect of Median Width on Highway
                         Accident Rates, Transportation Research Record 1401, 1993.




                         Page 46                                           GAO-03-436 Traffic Crash Causation
                        Appendix III: Roadway Design Features




                        and increasing widths continue to provide additional benefits up to widths
                        of approximately 65 to 80 feet.

Existence of Barriers   Some experts told us that although the installation of median barriers can
                        reduce head-on crashes, their presence may increase the number of total
                        crashes. This might occur because the median barrier reduces the amount
                        of space a vehicle has to recover within the median. The Washington State
                        Department of Transportation recently conducted a study of cross-median
                        crashes on multilane and divided state highways with full-access control.45
                        One goal of the study was to revise the guidelines for the installation of
                        median barriers. The study examined cross-median crashes from 1996
                        through 2000 from a sample of 677 miles of road. Using a benefit-cost
                        analysis, the study recommended installing median barriers on all
                        full-access control, multilane highways with posted speed limits of 45
                        miles per hour or greater where the median width was 50 feet or less.


Lane Widths             Wider lanes increase the separation between vehicles traveling in adjacent
                        lanes as well as provide additional space to recover from near-crash
                        situations. In a recent study, FHWA addressed the relationship between
                        lane width and crashes on two-lane rural highways based on expert
                        assessments and previous studies.46 The study included an analysis of the
                        combined effects of lane width and average daily traffic on crash rates,
                        and it predicted that lane width has only a slight impact on crash rates at
                        low volumes of traffic.47 However, the study also predicted that at
                        high-average daily traffic volumes, the two-lane rural roads with 9-foot
                        lanes have a 50 percent greater chance of having crashes than have similar
                        roads with 12-foot lanes. In discussing lane width with experts, we were
                        told by one academic researcher that while wider lanes provide additional
                        space between vehicles, wider lanes may give drivers an increased
                        perception of safety resulting in higher rates of speed, possibly leading to
                        other safety problems.




                        45
                          Washington State Department of Transportation, Median Treatment Study on
                        Washington State Highways (March 2002).
                        46
                         D.W. Harwood, F.M. Council, E. Hauer, W.E. Hughes, and A. Vogt, Prediction of the
                        Expected Safety Performance of Rural Two-Lane Highways, FHWA-RD-99-207 (December
                        2000).
                        47
                          This factor applies to single-vehicle run-off-the-road, multiple-vehicle same-direction
                        sideswipe crashes, and multiple-vehicle opposite-direction crashes.




                        Page 47                                                GAO-03-436 Traffic Crash Causation
                    Appendix III: Roadway Design Features




Roadway Shoulders   Roadway shoulders provide a clear space for drivers to recover from
                    errors. A recent FHWA study examined the relationship between shoulder
                    width, average daily traffic, and crash rates for two-lane rural highways
                    and predicted that, in general, at low-average daily traffic rates, shoulder
                    width only slightly affects the crash rate but as the average daily traffic
                    rate increases, so does the influence of shoulder width on crash rates.48
                    For example, at high-average daily traffic volumes, the study predicted
                    that a 50 percent greater number of crashes occur on two-lane rural
                    highways with no shoulders than on similar roads with 6-foot shoulders.
                    Experts told us that while wider shoulders are generally better than
                    narrow ones, the benefits that shoulders provide are also influenced by the
                    material from which they are constructed. A researcher at the University
                    of North Carolina’s Highway Research Safety Center told us that paved
                    shoulders are associated with fewer crashes at lower rates than those with
                    gravel or grass shoulders. Another expert pointed out that soft shoulders
                    can lead to a loss of vehicle control both through the uneven edges
                    between the driving lane and the shoulder or through a differential of
                    friction between the driving lane and the shoulder.


Curves              Curves have been shown to contribute to crashes, whether horizontal
                    curves (left or right) or vertical curves (up and down). Various elements of
                    curves may affect the likelihood of a crash, including features of the curve
                    (for example, degree, length, and angle of the curve) and cross-sectional
                    curve elements (for example, lane width, shoulder size and type.) A 1991
                    FHWA study identified factors more strongly associated with curves than
                    adjacent straightaways in Washington State.49 These factors included a
                    higher percentage of fatal crashes, head-on and opposite sideswipe
                    crashes, fixed-object and rollover crashes, crashes at night, and crashes
                    involving drinking drivers. Vertical curves have also been associated with
                    higher crash rates, though, according to an American Association of State
                    Highway and Transportation Officials chairperson, not as much as
                    compared with horizontal curves. An important design element regarding




                    48
                     D.W. Harwood, F.M. Council, E. Hauer, W.E. Hughes, and A. Vogt, Prediction of the
                    Expected Safety Performance of Rural Two-Lane Highways, FHWA-RD-99-207 (December
                    2000).
                    49
                      C. Zegeer, J. Stewart, F. Council, and D. Reinfurt, Cost Effective Geometric Improvements
                    for Safety Upgrading of Horizontal Curves, Federal Highway Administration Report
                    FHWA-RD-90-021 (October 1991).




                    Page 48                                              GAO-03-436 Traffic Crash Causation
                Appendix III: Roadway Design Features




                vertical curve safety is the need to provide drivers with adequate stopping
                sight distance.


Access Points   Access points are locations where vehicles enter a roadway, such as
                residential and business driveways and exit and entrance ramps on
                highways. A 1998 study completed for the Minnesota Department of
                Transportation found that as access points to roads increase, so do the
                number of crashes.50 For example, on four-lane urban conventional
                roadways, with no left turns, the researchers found that in Minnesota there
                were an average of 2.22 crashes per million vehicle miles traveled when
                there were from zero to ten access points per mile. (See fig. 11.) However,
                the rate of crashes increased to 7.38 when the number of access points
                was greater than 50 per mile. Additionally, traffic safety experts supported
                the conclusion that more access points generally lead to higher crash
                rates.




                50
                 Minnesota Department of Transportation, Statistical Relationship Between Vehicle
                Crashes and Highway Access (August 1998).




                Page 49                                            GAO-03-436 Traffic Crash Causation
                Appendix III: Roadway Design Features




                Figure 11: Impact of Access Points on Traffic Crashes




Intersections   According to FHWA, intersections are among the most complex roadway
                designs a driver encounters. A recent report for NHTSA found that in 2001,
                intersection and intersection-related crashes represented 22.5 percent of
                total fatal crashes and 43 percent of overall crashes.51 There are four major
                crash types at intersections: crossing, rear-end, improper lane changing,
                and pedestrian and bike. Multiple factors contribute to intersection
                crashes, including: poor physical design, inadequate traffic engineering,
                failure of driver licensing and education to train drivers in negotiating
                intersections, and driver disregard for traffic control devices. For example,
                a poorly designed intersection might provide inadequate sight distance,
                which could limit a driver’s response time to react to vehicles or
                pedestrians at that intersection. Additionally, incorrectly timed or
                inconspicuous traffic control devices can also contribute to a crash.




                51
                 National Highway Traffic Safety Administration, Traffic Safety Facts, 2001.




(545006)        Page 50                                             GAO-03-436 Traffic Crash Causation
                         The General Accounting Office, the audit, evaluation and investigative arm of
GAO’s Mission            Congress, exists to support Congress in meeting its constitutional responsibilities
                         and to help improve the performance and accountability of the federal
                         government for the American people. GAO examines the use of public funds;
                         evaluates federal programs and policies; and provides analyses,
                         recommendations, and other assistance to help Congress make informed
                         oversight, policy, and funding decisions. GAO’s commitment to good government
                         is reflected in its core values of accountability, integrity, and reliability.


                         The fastest and easiest way to obtain copies of GAO documents at no cost is
Obtaining Copies of      through the Internet. GAO’s Web site (www.gao.gov) contains abstracts and full-
GAO Reports and          text files of current reports and testimony and an expanding archive of older
                         products. The Web site features a search engine to help you locate documents
Testimony                using key words and phrases. You can print these documents in their entirety,
                         including charts and other graphics.
                         Each day, GAO issues a list of newly released reports, testimony, and
                         correspondence. GAO posts this list, known as “Today’s Reports,” on its Web site
                         daily. The list contains links to the full-text document files. To have GAO e-mail
                         this list to you every afternoon, go to www.gao.gov and select “Subscribe to daily
                         E-mail alert for newly released products” under the GAO Reports heading.


Order by Mail or Phone   The first copy of each printed report is free. Additional copies are $2 each. A
                         check or money order should be made out to the Superintendent of Documents.
                         GAO also accepts VISA and Mastercard. Orders for 100 or more copies mailed to a
                         single address are discounted 25 percent. Orders should be sent to:
                         U.S. General Accounting Office
                         441 G Street NW, Room LM
                         Washington, D.C. 20548
                         To order by Phone:     Voice:    (202) 512-6000
                                                TDD:      (202) 512-2537
                                                Fax:      (202) 512-6061


                         Contact:
To Report Fraud,
                         Web site: www.gao.gov/fraudnet/fraudnet.htm
Waste, and Abuse in      E-mail: fraudnet@gao.gov
Federal Programs         Automated answering system: (800) 424-5454 or (202) 512-7470


                         Jeff Nelligan, managing director, NelliganJ@gao.gov (202) 512-4800
Public Affairs           U.S. General Accounting Office, 441 G Street NW, Room 7149
                         Washington, D.C. 20548