Report to Congressional Requesters

United States General Accounting Office 

GAO 

March 2003 HIGHWAY SAFETY

Research Continues 

on a Variety of 

Factors That 

Contribute to Motor 

Vehicle Crashes 

GAO-03-436 
Many factors combine to produce circumstances that may lead to a 

motor 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 

automobile, including speeding and violating traffic laws, as well as being 

affected by alcohol or drugs, inattention, decision errors, and age. 

Roadway environment factors include the design of the roadway, 

roadside hazards, and roadway conditions. Vehicle factors include any 

failures that may exist in the automobile or design of the vehicle. Human 

factors are seen as the most prevalent, according to data, experts, and 

studies, in contributing to crashes, followed by roadway environment 

and vehicle factors. 

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 conducting a 

study on the causes and contributing factors to large truck crashes. In 

addition, the National Highway Traffic Safety Administration is 

conducting a 100-Car Naturalistic Driving Study and the Drive Atlanta 

Study. The 100-Car Naturalistic Driving Study involves collecting data 

from vehicles equipped with sensors and cameras to obtain better 

information on crashes and near misses. The Drive Atlanta Study 

involves collecting data from 1,100 vehicles equipped with data recorders 

to develop information about how excessive speed contributes to 

crashes. 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 study, among other 

things, would involve installing sensors and other data collection devices 

on over 5,000 vehicles. 

Fatality Statistics, 1975–2001 

HIGHWAY SAFETY 

Research Continues on a Variety of 

Factors That Contribute to Motor Vehicle 

Crashes 

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. 

Highlights of GAO-03-436, a report to 

congressional requesters 

March 2003

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. Since the 1970s, 

progress has been made in 

reducing the number of fatalities 

and injuries on our nation’s roads. 

From 1975 through 2001, fatalities 

decreased from 44,525 to 42,116, 

while the rate of fatalities per 100 

million vehicle miles traveled 

decreased from 3.35 to 1.51. 

However, the decline in fatalities 

has leveled off in recent years. In 

the 1970s, Indiana University 

conducted one of the most 

significant studies to date on the 

factors that contribute to motor 

vehicle crashes. This study 

examined human, environmental, 

and vehicle factors that contribute 

to crashes. As requested, this 

report provides more recent 

information from data, experts, and 

studies about the factors that 

contribute to motor vehicle crashes 

and information about major 

ongoing and planned Department 

of Transportation research into 

factors that contribute to crashes. 
Page i GAO-03-436 Traffic Crash Causation 

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 TriLevel Study 44

Figure 11: Impact of Access Points on Traffic Crashes 50

Contents 
Page ii 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 1 GAO-03-436 Traffic Crash Causation 

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. 

United States General Accounting Office

Washington, DC 20548 
Page 2 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 

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. 

Results in Brief 
Page 3 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 

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 propertydamage-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. 

Background 
Page 4 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 TriLevel 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 policereported 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 5 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 TriLevel 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 6 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. 

For example, it would be challenging to identify a single cause of a crash 

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 

would likely be the combined effect of a number of these factors that 

contributed to the crash. 

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 

Human, Roadway 

Environment, and 

Vehicle Factors 

Contribute to Motor 

Vehicle Crashes 
Page 7 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 involve actions taken by or the condition of the driver of 

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. 

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. 

Human Factors Contribute 

to Motor Vehicle Crashes 

Speeding 
Page 8 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 PostNMSL Era (Washington, D.C.: February 1998). 
Page 9 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 crashinvolvement 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 10 GAO-03-436 Traffic Crash Causation 

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.

Traffic Control Violations 
Page 11 GAO-03-436 Traffic Crash Causation 

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 alcoholrelated 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. 

 10Blood alcohol content of .08 percent in Massachusetts is evidence of alcohol impairment, 

but it is not illegal per se. 

11Of these states, Louisiana, New York, and Tennessee have .08 percent BAC laws that will 

be effective during the latter half of 2003. 

12NHTSA 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. 

Alcohol and Other Drugs 
Page 12 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, 

 13H. 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 13 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

 14The 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. 

15P.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). 

16The 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. 

17These 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 14 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 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. 

 18Examples 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). 

19Hindrik W. J. Robbe and James F. O’Hanlon, Marijuana, Alcohol, and Driving 

Performance (The Netherlands: Institute for Human Psychopharmacology, July 1999). 

20C.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). 

Driver Inattention 
Page 15 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. 

 21About 6 million were identified as “unknown” or “no driver present.” 
Page 16 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 

 22Jane 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 17 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 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. 

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 

 23The 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. 

24D. 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. 

Driver Decision Errors 

Age 
Page 18 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 

 25For 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 19 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 

 26A.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. 

27Guohua 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). 

28Leonard Evans, “Age and Fatality Risk from Similar Severity Impacts,” Journal of Traffic 

Medicine, vol. 29, 2001, pp. 10–19. 
Page 20 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. 

The roadway environment is generally cited as the second most prevalent 

factor contributing to crashes by data, experts, and studies. It can be 

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). 

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 

 29David 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). 

30Kenard 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). 

Roadway Environment 

Contributes to Motor 

Vehicle Crashes 

Roadway Design 
Page 21 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. 

 31The 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 22 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. 

 32D.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 23 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 24 GAO-03-436 Traffic Crash Causation 

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 runoff-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 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 

 33Jinsun Lee and Fred Mannering, Analysis of Roadside Crash Frequency and Severity 

and Roadside Safety Management, Washington State Transportation Center (December 

1999). 

Roadside Hazards 

Roadway Conditions 
Page 25 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 

 34Keith 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). 

35Federal Highway Administration, Comparison of the Safety of Lighting Options on 

Urban Freeways, FHWA Public Roads On-Line (Autumn 1994). 
Page 26 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 can contribute to crashes through vehicle-related failures 

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. 

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 equipmentrelated failures might lead to the loss of a vehicle’s handling capabilities, 

Vehicle Factors Contribute 

to Motor Vehicle Crashes 

Vehicle-Related Failures 
Page 27 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. 

The design of a vehicle has been shown to affect handling in particular 

types of maneuvers. For example, high-performance sports cars have very 

Vehicle Design 
Page 28 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. 

 36For this VMT analysis we used data from the 2001 National Household Travel Survey. 
Page 29 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 30 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 

 37National Transportation Safety Board, Evaluation of the Rollover Propensity of 15-

Passenger Vans, NTSB SR-02/03 (October 2002). 
Page 31 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 singlevehicle 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 

 38Charles 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. 

39William Deutermann, Characteristics of Fatal Rollover Crashes, DOT HS 809 438 (April 

2002). 

40This 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 32 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 

research projects underway and planned that address aspects of crash 

causes. For example, the Federal Motor Carrier Safety Administration and 

NHTSA are conducting a study on the causes and contributing factors to 

large truck crashes. NHTSA is also funding the 100-Car Naturalistic 

Driving Study, which involves collecting data about crashes and near 

misses from 100 vehicles equipped with sensors. Further, NHTSA is 

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. 

In 1999, Congress established the Federal Motor Carrier Safety 

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 costeffective countermeasures can be developed to decrease the number and 

severity of these crashes. 

Federal Research 

Directed at Better 

Understanding of 

Factors That 

Contribute to Crashes 

Large Truck Crash 

Causation Study 
Page 33 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. 

NHTSA is currently conducting the 100-Car 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 

One Hundred-Car 

Naturalistic Driving Study 
Page 34 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. 

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 

Drive Atlanta Study 
Page 35 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. 

In the Transportation Equity Act for the 21st Century (P.L. 105-178), 

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 

Future Strategic Highway 

Research Program 
Page 36 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 largescale instrumented vehicle study to identify appropriate countermeasure 

improvements. 

We provided copies of a draft of this report to the Department of 

Transportation for its review and comment. In discussing this report, 

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. 

 41In 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. 

Agency Comments 

and Our Evaluation 
Page 37 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 
Appendix I: Objectives, Scope, and 

Methodology 

Page 38 GAO-03-436 Traffic Crash Causation 

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 

data for calendar years 1997 through 2001 from NHTSA’s crash reporting 

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 

Appendix I: Objectives, Scope, and 

Methodology 

Analyzing NHTSA 

Data 
Appendix I: Objectives, Scope, and 

Methodology 

Page 39 GAO-03-436 Traffic Crash Causation 

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 
Appendix I: Objectives, Scope, and 

Methodology 

Page 40 GAO-03-436 Traffic Crash Causation 

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 

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 

 422001 National Household Travel Survey User’s Guide, Version 1(Preliminary Release) 

January 2003. 

Identifying Studies 
Appendix I: Objectives, Scope, and 

Methodology 

Page 41 GAO-03-436 Traffic Crash Causation 

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 

and other experts. Within DOT, we interviewed officials from the Volpe 

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 

contribute to motor vehicle crashes, we interviewed officials from NHTSA, 

FHWA, and the Transportation Research Board. These agencies have a 

great deal of ongoing and planned research on a wide variety of motor 

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. 

Interviewing Federal 

Officials and Experts 

Ongoing and Planned 

Transportation 

Research 
Appendix II: Tri-Level Study of the Causes of 

Traffic Accidents 

Page 42 GAO-03-436 Traffic Crash Causation 

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 

NHTSA’s needs for data on traffic crash causation. Two of the main 

objectives for the research were to: 

• 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 

Appendix II: Tri-Level Study of the Causes of 

Traffic Accidents

Objectives, Scope, 

and Methodology for 

the Tri-Level Study 
Appendix II: Tri-Level Study of the Causes of 

Traffic Accidents 

Page 43 GAO-03-436 Traffic Crash Causation 

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 

categories, and vehicle factors the least frequently implicated. As figure 10 

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. 

Results of the TriLevel Study 
Appendix II: Tri-Level Study of the Causes of 

Traffic Accidents 

Page 44 GAO-03-436 Traffic Crash Causation 

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 severityincreasing 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. 

The study categorizes human direct causes based on an informationprocessing 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 

Human Factors 
Appendix II: Tri-Level Study of the Causes of 

Traffic Accidents 

Page 45 GAO-03-436 Traffic Crash Causation 

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. 

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. 

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. 

Environmental Factors 

Vehicle Factors 
Appendix III: Roadway Design Features 

Page 46 GAO-03-436 Traffic Crash Causation 

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 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. 

An analysis of NHTSA’s databases showed that from 1997 through 2001, 44 

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. 

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, 

 43Kenneth Agent and Jerry Pigman, Safety Impacts of Rural Road Construction, Kentucky 

Transportation Center KTC-01-01(February 2001). 

44M.W. Knuiman, F.M. Council, and D.W. Reinfurt, The Effect of Median Width on Highway 

Accident Rates, Transportation Research Record 1401, 1993. 

Appendix III: Roadway Design Features 

Medians 

Presence or Absence of 

Medians 

Width of Medians 
Appendix III: Roadway Design Features 

Page 47 GAO-03-436 Traffic Crash Causation 

and increasing widths continue to provide additional benefits up to widths 

of approximately 65 to 80 feet. 

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. 

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. 

 45Washington State Department of Transportation, Median Treatment Study on 

Washington State Highways (March 2002). 

46D.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). 

47This factor applies to single-vehicle run-off-the-road, multiple-vehicle same-direction 

sideswipe crashes, and multiple-vehicle opposite-direction crashes. 

Existence of Barriers 

Lane Widths 
Appendix III: Roadway Design Features 

Page 48 GAO-03-436 Traffic Crash Causation 

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 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 

 48D.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). 

49C. 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). 

Roadway Shoulders 

Curves 
Appendix III: Roadway Design Features 

Page 49 GAO-03-436 Traffic Crash Causation 

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

sight distance. 

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. 

 50Minnesota Department of Transportation, Statistical Relationship Between Vehicle 

Crashes and Highway Access (August 1998). 

Access Points 
Appendix III: Roadway Design Features 

Page 50 GAO-03-436 Traffic Crash Causation 

Figure 11: Impact of Access Points on Traffic Crashes 

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. 

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

Intersections 

(545006) 
The General Accounting Office, the audit, evaluation and investigative arm of 

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 

through the Internet. GAO’s Web site (www.gao.gov) contains abstracts and fulltext 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 

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. 

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: 

Web site: www.gao.gov/fraudnet/fraudnet.htm 

E-mail: fraudnet@gao.gov

Automated answering system: (800) 424-5454 or (202) 512-7470 

Jeff Nelligan, managing director, NelliganJ@gao.gov (202) 512-4800 

U.S. General Accounting Office, 441 G Street NW, Room 7149 

Washington, D.C. 20548 

GAO’s Mission 

Obtaining Copies of 

GAO Reports and 

Testimony 

Order by Mail or Phone 

To Report Fraud, 

Waste, and Abuse in 

Federal Programs 

Public Affairs