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.
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).
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?
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. Salient factors that contribute
to the incidence aggressive driving.
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.
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.
DISREGARD FOR OTHERS AND
DISREGARD FOR THE LAW
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.
HABITUAL OR CLINICAL BEHAVIOR
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.
SUMMARY OF CONTRIBUTING
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