This report presents the results of a study conducted for the National Highway Traffic Safety Administration (NHTSA) to assess the effects of two programs that were implemented to reduce the incidence of aggressive driving. This brief introduction discusses the reasons for conducting the study. Subsequent sections of the report are devoted to descriptions of the countermeasure programs, the results of the programs, and the implications of study results.

The words, “aggressive driving,” emerged during the 1990s as a label for a category of dangerous on-the-road behaviors. The category comprises following too closely, driving at excessive speeds, weaving through traffic, and running stop lights and signs, among other acts. Aggressive driving occasionally escalates to gesturing in anger or yelling at another motorist, confrontation, physical assault, and even murder; “Road Rage” is the label that emerged to describe the angry and violent behaviors at the extreme of the aggressive driving continuum. NHTSA defines aggressive driving as, “The operation of a motor vehicle in a manner that endangers or is likely to endanger persons or property.” An important distinction is that aggressive driving is a traffic violation, while road rage, aside from the yelling and gesticulating, is a criminal offense.

People have reported the occasional on-the-road behavior that we now describe as aggressive driving since the advent of motorized transport, and quite possibly, since the beginning of vehicular travel. Anyone who has spent more than a few hours in an automobile has experienced the rudeness of other drivers. Until the final decade of the Twentieth Century, most motorists were comforted by knowing that aggressive driving behavior was infrequent and atypical, and that extreme, confrontational acts were quite rare. However, beginning in the 1990s, an unrelenting series of news reports captured the public’s attention and elevated to a national problem what previously had been considered to be, simply, rude and occasionally bizarre human behavior.1

The shocking reports of road rage incidents appeared to many observers to coincide with a noticeable increase in aggressive driving, in general, and a sharp decline in civility and respect for other motorists and traffic laws. The AAA Foundation for Traffic Safety studied more than 10,000 reported cases of road rage and found a 51 percent increase in serious incidents between 1990 and 1996 (Mizell, 1997). A national survey found that 60 percent of motorists believe that unsafe driving by others is a major personal threat to them and their families; 75 percent of the respondents consider it to be “very important” to do something about unsafe driving (NHTSA, 1999).

It is reasonable to question the claims of dramatic increases in aggressive driving and road rage. For example, Mizell’s estimate of a 51 percent increase in extreme cases was based on news reports, but the amount of reporting on a topic in a particular year is influenced by journalists’ interest in an issue, not necessarily the actual incidence of the phenomenon in question. Even accepting Mizell’s estimate of 10,000 cases of road rage during the first six years of the 1990s, the incidence is really quite low compared to the numbers of injuries and fatalities that occur on our nation’s roads and highways. During the same six year period studied by Mizell, more than 22.7 million people were injured in motor vehicle crashes in the U.S., and more than 290,000 people were killed (FARS, 2000). That is, the number of cases of road rage was only .04 percent of the total number of people injured or killed in traffic (i.e., four one-hundredths of a percent), or one case of road rage for every 2,300 injuries and fatalities. The relative size of the road rage problem is further revealed by comparisons to subsets of traffic crash data. For example, 33,521 pedestrians and 4,782 bicyclists were killed, and 531,000 pedestrians and 385,000 bicyclists were injured during the six year period in which Mizell counted 10,000 cases of road rage with various outcomes (FARS, 2000).

The crash data suggest that road rage is a relatively small traffic safety problem, despite the volume of news accounts and the general salience of the issue. It is important to consider the issues objectively because programmatic and enforcement efforts designed to reduce the incidence of road rage might detract attention and divert resources from other, objectively more serious traffic safety problems. Although cases of road rage are relatively rare, the incidence of aggressive driving is much more frequent and a measurable contributing factor to traffic crashes.

The perceived increase in aggressive driving is largely explained by demographic changes. In particular, the population of the United States increased by nearly 100 million people between 1960 and the year 2000, and by 35 percent since 1970, the year that NHTSA was created with the mission of improving traffic safety. Traffic safety has improved significantly, with fatality rates declining from 5.5 per million miles traveled during the mid-1960s to 1.5 fatalities per million miles traveled in the year 2000. Figure 1 illustrates the change in fatality rate since 1966 (FARS, 2000).

The numbers presented in Table 1 show that the final decade of the Twentieth Century was a period of rapid population growth, with even greater increases in individual mobility and improvements in the ultimate measure of traffic safety. The table shows that the population of the U.S. increased by 22 million people between 1991 and the year 2000, an increase of nine percent. However, the number of licensed drivers increased by 21 million during the same period (an increase of 13 percent), and there were 30 million additional vehicles (an increase of 16 percent) and nearly 600 billion additional miles traveled in the year 2000 than in 1991 (an increase of 27 percent). That is, the number of miles traveled in a year increased at a rate that is three times the rate of population growth. The table also shows that despite the 27 percent increase in miles traveled between 1991 and the year 2000, a driver was 21 percent less likely to die in a motor vehicle crash at the end of the decade than at the beginning. In other words, it is safer to drive on our nations roads and highways now than ever before, despite the increases in population, miles traveled, and aggressive driving. How is this possible?

Figure 1 - click "d" for long descriptiond

Figure 1. Fatality rates per 100 million miles traveled in the U.S.


United States
Fatalities Per
100 Million Miles
Sources: FARS 2000, US Census

Improved safety features of vehicles and highways, and a general aging of the population, have contributed incrementally to the steady decline in the traffic fatality rate. However, since 1980, the greatest contributions to the improved conditions have come from law enforcement efforts, in particular, a focus on detecting and removing impaired drivers from the road and the development of general deterrence and effective public information and education (PI&E) programs. Largely in response to the enforcement and programmatic efforts, the proportion of all crashes in which alcohol was involved declined by 25 percent during the 1990s; there were 3,200 fewer alcohol-related traffic fatalities in the year 2000 than in 1991, even though the numbers of drivers, vehicles, and miles traveled all increased substantially. Law enforcement and traffic safety experts believe that some of the methods that helped reduce the incidence of alcohol-involved crashes also might be useful for reducing the number of crashes caused by aggressive driving.

A definitive explanation for aggressive driving is beyond the scope of the current study. However, a brief discussion of contributing factors might be useful to understanding study results. Experts have suggested many reasons for the apparent increases in aggressive driving and road rage. Sociologists point to the fragmentation of society and the disintegration of shared values and sense of community as the cause of these and other acts of incivility. Many psychologists blame the intoxicating combination of power and anonymity provided by motor vehicles. Traffic engineers tend to ignore the human component, recognizing that crashes can occur when a vehicle that is traveling at the design speed of a roadway encounters a slower moving vehicle. The engineering solution is to encourage all drivers to travel at uniformly fast speeds to avoid the potentially dangerous encounters, but this approach disregards different perceptions of conditions and differences in motorists’ destinations, intentions, and capabilities.

Many law enforcement officers have learned from their operations-level experiences with dangerous drivers that several factors can contribute to a single example of aggressive driving. Further, it is important to understand that not all instances of the behaviors that are categorized as aggressive driving are volitional. For example, errors in judging turning headway can result in right of way violations, and driver inattention can result in failures to obey traffic signals and signs. Also, driving in excess of a speed limit does not always endanger persons or property, nor does it necessarily involve an aggressive intent. That is, an unknown portion of all such driving acts is caused by human error, rather than conscious decisions to take risks and drive aggressively. Figure 2 illustrates the most salient factors, excluding human error, that are believed to contribute to the apparent increase in the incidence of aggressive driving behavior. The factors are summarized in the following paragraphs.

Figure 2 - click "d" for long descriptiond

Figure 2. Salient factors that contribute to the incidence aggressive driving.

Traffic congestion is one of the most frequently mentioned contributing factors to aggressive driving. On-the-road delays, whether caused by highway maintenance, a collision, or high traffic volumes, are frustrating for all drivers, but intolerably so for some. Drivers with low tolerances for traffic delays might respond by following too closely, changing lanes frequently, or becoming angry at anyone who impedes their progress. A 1998 survey found that 33 percent of drivers reported that they become impatient while waiting at stoplights and for parking spaces; 25 percent reported impatience while waiting for passengers to enter their vehicle; and, 22 percent said that they feel anger when a multi-lane highway narrows (Ferguson, 1998).

The survey results concerning driver impatience and anger are particularly revealing when considered in the context provided by Table 1, and one additional statistic. That is, while the number of miles traveled increased by 27 percent during the 1990s, the number of miles of roadway in the United States increased by only one percent. Together, these measures confirm and quantify most drivers’ subjective perceptions; traffic congestion has, indeed, increased.

Some people drive aggressively because they have too much to do and are “running late” for work, school, their next meeting, lesson, soccer game, or other appointment. There does, indeed, appear to be more to do with each passing year. It is reported that the average mother now spends more than an hour making five trips and driving 29 miles during a typical day. Many of the stops are to drop off or pick up children or elderly parents who cannot drive themselves (STPP, 2002). The endless series of errands and obligations of modern life weighs more heavily and/or more frequently on some individuals than on others, and can contribute to a pattern of aggressive driving. The effects of busy schedules on driving were evident when several police departments in the Washington, DC, area conducted a special enforcement program that targeted aggressive drivers. Officers issued approximately 60,000 citations during a 28 day period in 1997 for offenses ranging from following too closely to passing on the right. The most frequent excuse offered by the violators was, “I’m late” (Ferguson, 1998).

Driving involves a unique combination of public and private behavior. A motor vehicle insulates the driver from the world while, at the same time, traveling through it. Shielded from the hostile outside environment by tinted windows and a micro-climate that defies the seasons, a driver can develop a sense of anonymity and detachment, as if an observer of the surroundings, rather than a participant. The anonymity provided by this insulation can erode the inhibitions to antisocial behavior that normally shape interpersonal relations. That is, some people feel less constrained in their behavior when they cannot be seen by others and/or when it is unlikely that they will ever again see the witnesses to their behavior. When emboldened by the seemingly invincible power of a motor vehicle, a driver’s feeling of anonymity can result in extreme rudeness and even transform an otherwise nice person into a dangerous, raging individual.2
Ellison et al. (1995) tested the hypothesis that vehicle-induced anonymity contributes to aggressive behavior, wisely limiting the dependent variables to measures of relatively harmless horn honking. Convertibles and jeep-like vehicles were delayed at controlled intersections by an automobile, operated by a confederate of the experimenters, that failed to proceed when the light changed to green. The confederate recorded whether the top on the delayed convertible (immediately behind the confederate’s vehicle) was up (the anonymous condition) or down (the exposed or identifiable condition). Several additional variables were recorded, including the gender and age of the driver, the number of passengers, and the type of vehicle. The confederate also recorded the time interval between the change to the green light and the first sounding of the convertible’s horn, the number of honks, and the duration of the honking. As predicted, the experimenters found that drivers in the anonymous condition (convertible tops up) honked significantly sooner, more frequently, and for longer durations than the drivers in the exposed condition (tops down).

Gulledge (1996) modified the research design by using a convertible as the impeding vehicle at intersections, with the convertible’s top up for half of the trials and the top down for the other half. Only the time interval between the light change and the first honk by the delayed driver (any passenger vehicle located immediately behind the experimenter’s convertible) was recorded. Analysis of the data found significantly longer intervals between the light change and the first use of the horn when the top on the delaying convertible was down, exposing the experimenter and driver to view. The results of this study suggest that greater visibility of the intended target also inhibits horn honking, and that mutual anonymity is a factor in at least some aggressive driving behaviors.

Human behavior is clearly shaped by the external forces collectively known as Culture. The external source of the influence and degree to which norms can change are illustrated by the music, clothing, or salutation that seemed so “stylish” or appropriate in 1970, and so odd or inappropriate now. All forms of human behavior, including driving style, are similarly influenced by external forces that define what is appropriate and what is not, and the definitions change over time.

Feature films and television programming can be extremely influential in defining current style and appropriate or desirable behavior. The extent of media influence on popular culture and behavior is not fully understood. In particular, it is unknown if depictions of car chases influence motorists to drive aggressively by gradually altering individual conceptions of acceptability, or more immediately, by providing vivid images of aggressive behavior for motorists to model. Children predictably exhibit the aggressive behavior observed previously in a cartoon; it is likely that some adults and adolescents of driving age are similarly influenced by the driving observed in films and on television.3 Learning to drive from a parent or friend who is an aggressive driver, or associating with aggressive drivers, also can shape the behavior. In this regard, Parker et al. (1998) found that drivers who had committed large numbers of aggressive driving violations were more likely to believe that people important to them would approve of the behavior, than drivers with few violations.
Much has been written about the erosion of shared values and respect for authority, variously attributed to the fragmentation of the extended family, increased individual mobility, media influence, and other characteristics of modern society. It does appear that civility and respect for authority have diminished, the trend epitomized by the phrase, “I’m just looking out for number one.”

Most motorists rarely drive aggressively, and some never at all. For others, episodes of aggressive driving are frequent, and for a small proportion of motorists it is their usual driving behavior. Occasional episodes of aggressive driving might occur in response to specific situations, such as speeding and changing lanes abruptly when late for an important appointment, when it is not the driver’s normal behavior. Among the chronic aggressive drivers there are those who learned the driving style and consider it appropriate, and others who may have learned to drive properly, but for whom the behavior is an expression of illness. Clearly, it is a matter of degree and not all anger is uncontrolled, or even inappropriate; that is, it is not the anger, but what a person does about it that matters (e.g., anger that motivates a person to call the police when encountered on the road by an obviously impaired or dangerously aggressive driver). However, chronic anger, habitual or persistent aggressive driving, and especially a pattern of confrontation on the road, must be considered manifestations of pathology, in addition to violations of the law.4

The less extreme forms of aggressive driving are better understood, but are we really experiencing increases in road rage and aggressive driving? The answer is “yes,” and for the same reason that traffic congestion has increased, as described previously in the Introduction to this report and summarized in Table 1. That is, even if the proportions of predisposed and provoked drivers have remained unchanged during the past decade, 26 percent increases in both road rage and aggressive driving should be expected from the increase in miles traveled during that period (i.e., a 27 percent increase in miles traveled minus a one percent increase in new roadway); rate and incidence of the phenomena are separate measures. If it seems that there are more cases of rude and outrageous behavior on the road now than in the past, the observation is correct, if for no other reason than there are more drivers driving more miles on the same roads than ever before.

The preceding discussion addressed only the most salient of the many factors that might contribute to the incidence of road rage and aggressive driving. Sociologists, psychologists, psychiatrists, journalists, traffic safety experts, and law enforcement personnel, among others, all have offered opinions concerning the causes of road rage and aggressive driving. Some of the suggested causes are more likely to help explain the behavior than others.

Scott (2002) assembled an inventory of diverse contributing factors to aggressive driving, ranging from violent video games to increased commuting distances and durations. We have added to Scott’s inventory of contributing factors, based on the current research, and present the modified list in Appendix A of this report. The large number and diversity of possible causes of aggressive driving implies that the behaviors are complex and could be influenced by many different predisposing and provoking factors.

1For example, following separate disputes in traffic: a Massachusetts bookkeeper murders another motorist with a single shot from a crossbow; a soccer mom runs another woman off the road, and to her death, in Mississippi; two Virginia men crash into oncoming traffic, killing three drivers, as the final act of an angry, on-the-road duel; a Maryland lawyer punches a pregnant woman after a minor fender-bender; in California, a famous actor uses a golf club to repeatedly smash the window and roof of a vehicle that cut him off in traffic; a driving instructor in North Carolina tells his student to chase a vehicle that cut them off and subsequently punches the offending driver; a high-school athlete is shot to death over a stop sign right-of-way dispute in New Mexico, and the incident is quickly followed by two more local fatalities attributed to “road rage.”

2 Perhaps the elevated perspective from the driver’s seat of a sport utility vehicle (SUV) contributes to feelings of both anonymity and invincibility, a hypothesis worthy of testing. Further, many sport utility vehicles seem to be designed more for war than civilian transportation. In this regard, the term “urban assault vehicle,” frequently used to describe SUVs, is strangely appropriate, particularly in the context of the familiar metaphors, “fighting traffic” and “it is a jungle out there.”

3 Composing this sentence evokes memories of revving engines and squealing tires as vehicles exited the parking lot following showings of the films, Grand Prix, in 1966, and Bullit, in 1968. Do modern films have this effect on young drivers?

4 Perhaps road rage, air rage, and office rage (i.e., “going postal”) are just different versions of the same phenomenon.