Better to see Chapter 16 Vision for a safer tomorrow    of Traffic Safety  (2004)

 

Chapter 15.  CONCLUSIONS (From 1991 book Traffic Safety and the Driver)

Below is only words of 1991 book -- the typeset pages may be viewed at no cost by clicking here

            This final chapter summarizes what I think are the most important overall conclusions arrived at in the earlier chapters.

            Traffic crashes constitute one of the largest public health problems in industrialized countries.  In the US almost half of the deaths to 19-year olds are due to traffic crashes; the total number of preretirement years of life lost due to traffic crashes is similar to that due to the combined effects from the two leading diseases, cancer and heart disease.

            Age and sex have a large influence on essentially all variables, such as the number of driver or pedestrian fatalities per capita, important in traffic safety.  One finding important for traffic safety, as well as for many areas unrelated to traffic, is that the risk of death from the same impact, or physical insult, depends strongly on age and sex.  From about age 15 to age 45, the same physical insult is approximately 25% more likely to kill a female than a male of the same age.  For ages greater than about 20, fatality risk grows at an approximately uniform rate of 2.3% per year for males and 2.0% per year for females; at age 70 the risk is about three times what it is at age 20.  Thus, as drivers become older, they face increasing risks of death in crashes of the same severity.  Although the risk of crashing increases as age increases beyond 40, older drivers still have fewer crashes per capita than do 20-year-old drivers.  Older drivers are involved in fewer crashes in which pedestrians are killed than are younger drivers.  The main reason why older drivers pose a reduced risk to other road users is that they drive less.  Thus the problem faced by the ageing driver may be more one of reduced mobility than of reduced safety.

            Vehicular factors are difficult to examine because, for example, more injuries per vehicle for one type of vehicle than another may reflect a difference in the types of drivers choosing one of the vehicles rather than a difference in vehicle crashworthiness.  Vehicle mass, or size, is the one vehicle characteristic that has the largest effect on injury and fatality risk in crashes.  Mass effects are large for single-car crashes as well as for multiple-vehicle crashes.  A driver switching to a heavier car receives a larger safety increase than the safety reduction sustained collectively by the other road users into which the heavier car might crash.  Federal Motor Vehicle Safety Standards appear to have reduced occupant fatality risk by about 15 to 20%.  The magnitudes of differences in fatality rates between different types of roads, in some cases over a factor of nine, suggest strongly that, say, replacing a stretch of rural two-lane roadway with a divided freeway reduces casualties substantially.  Fatalities per unit distance of travel are lower in the winter months, notwithstanding more hours of darkness, snow and ice.  Indeed, fatality risk is less on wet and snow-covered roads than on dry roads because drivers alter their behavior to reduce crash risk;  crash rates still increase, but fatalities decrease more because of lower speeds.  Thus inclement weather reduces mobility by deterring travel or reducing speeds more than it changes safety.  Fatality rates are dramatically higher at night than in the day, an effect largely due to such road-user characteristics as alcohol use.  Multi-disciplinary post-crash investigations in the US and UK identify road-user characteristics as factors in 94% and 95% of crashes, respectively.

            One of the most remarkable features of the driving task is that in a few months just about everybody can learn to perform it in a least a rudimentary fashion.  There is no clear relationship between safety and driving skill or knowledge.  The very groups with the highest levels of perceptual-motor skills
and interest in driving, racing drivers, young drivers, and male drivers, are the very groups with higher than average crash rates.  What is crucial is not how the driver can drive (driver performance), but how the driver does drive (driver behavior).  The overinvolvement of youth, and males, in traffic crashes is quantitatively similar to the overinvolvement of youth, and males, in criminal activity unrelated to traffic.  Observations of actual drivers show higher levels of risk taking are associated with these same groups.  Many studies provide evidence supporting the general contention that people drive as they live.  Involvement in traffic crashes is correlated with being emotionally unstable, unhappy, asocial, anti-social, impulsive, aggressive, unmarried, under stress, or other similar conditions.

            Alcohol plays a larger role in traffic safety than any other single factor.  About 10% of property damage, 20% of injuries and 47% of fatalities from traffic crashes would not occur were it not for alcohol.  Large though the losses due to alcohol are, they would be considerably larger were it not for the implementation in the past of many countermeasures.  Important amongst these is the development of "per se" laws which proscribe driving with an amount of alcohol in the blood in excess of some specified legal limit, typically 0.1% in the US, but lower almost everywhere else, and in some cases substantially lower (Sweden uses 0.02%).  More potentially important in the future than laws aimed specifically at individuals violating drunk driving laws are changes in the broader social context.  Drunk driving in the US appears intrinsically linked to overall national alcohol consumption; large reductions in drunk driving necessarily require reductions in alcohol consumption.  Increases in price and in difficulty of obtaining, and decreases in advertising, all lead to reduced alcohol consumption.

            Given that a crash occurs, a driver wearing a lap/shoulder belt is 42% less likely to be killed.  If the same driver is also protected by an airbag,
the risk is reduced by 47%; that is, the airbag prevents about 9% of the belted-driver deaths.  The airbag alone reduces fatality risk by 18% for drivers not wearing belts; all manufacturers advise that lap/shoulder belts must still be worn in airbag equipped cars.  A formerly belted driver who switches to airbag-only protection increases fatality risk by 41%.  Laws mandating the use of belts reduce fatalities, but by lesser amounts than a simple back-of-the envelope calculation indicates.

            Road-users often react to safety changes in traffic systems.  Examples in the literature show that, because of such reactions, interventions aimed at increasing safety have produced observed effects that have varied all the way from larger than expected safety increases to perverse effects (actual decreases in safety).  Similarly varied responses have been observed for changes, instituted for economic or other reasons, which were expected to reduce safety.  Some such interventions decreased safety more than expected while others generated perverse effects (actual increases in safety).  Although no model exists which can predict the actual safety effect of a new intervention, the results of prior interventions suggest some fairly stable patterns.  Vehicle technology changes which reduce crash risk in ways readily apparent to drivers are almost certain to be used to increase mobility.  Thus better brakes, handling, poor-weather vision, and drowsiness detection are expected to lead to faster driving, faster cornering, faster speeds under low visibility, and longer-duration driving; there is no way to know, short of empirical determination, whether any such specific technology will lead to a net increase or decrease in safety.  There is no evidence in the literature of measurable user responses to interventions that influence only the outcome of crashes, such as the use of safety belts or motorcycle helmets.  The possibility of user response is particularly implausible when the user is unaware of the safety intervention, as in the case of such crashworthiness
features as energy-absorbing steering columns and side-guard beams in doors.

            Traffic crashes should not be considered analogous to any specific disease, because this can invite the false hope that the problem might be solved by the sort of elegant knock-out blow that eliminated smallpox or scurvy.  Any such hope can tend to deflect attention and resources from realistic to unrealistic approaches.  A much more fruitful analogy is to all diseases.  Improvements in traffic safety, as in public health, are produced by a rich variety of interventions, a few making large contributions, but many more making important small contributions.  Any intervention which reduces US traffic fatalities by 1% prevents 450 deaths per year, a total that in contexts other than traffic would be considered enormous, not small.

            I consider that the largest potential for increases in traffic safety is in the realm of stimulating changes in social norms pertaining to road-user behavior.  While this is extremely difficult to quantify, it offers the possibility of larger increases than attainable by specific interventions.  For example, all US motorcyclists not wearing helmets becoming wearers would reduce US traffic fatalities by under 1%.  Equipping all cars with driver airbags, compared to no cars being so equipped, would reduce US traffic fatalities by 5%.  In contrast, changes in the role of alcohol in the US from 1982 to 1987 are estimated to have already generated a 12% reduction in traffic fatalities.  These changes are partially due to legislation, but are likely even more due to changing social norms brought about by synergistic effects of law changes and widespread discussion of the problem which made drinking and driving increasingly unacceptable behavior.

            It is clear that large improvements in public health have been generated by collective human behavior changes in smoking, exercise, diet, and alcohol use.  This leads me to conclude that the largest potential gains in traffic safety can be achieved by encouraging and stimulating changes in the social
norms relating to driving in directions more conducive to safety, and away from directions which are inimical to safety.  The following three factors seem likely to have important influences on social norms relating to driving; (1) fictional television and movie portrayals of the life-threatening use of motor vehicles as heroic, glamorous, humorous, or non-dangerous; (2) the encouragement of increased courtesy on the road, and (3) alcohol taxation and advertising policy, especially its influence on beer consumption by young male drivers.

            It is well recognized that good health is not just the business of doctors, hospitals, and medical researchers.  No matter how good the medical infrastructure, people cannot expect to be healthy if they smoke, overeat, abuse drugs, and do no exercise, in the expectation that the system will take care of them.  It must similarly become recognized that traffic safety is not just the concern of road and vehicle builders, police, legislators, and government regulators.  This is in no way to undervalue the importance, let alone responsibility, of such bodies, but to stress that traffic safety, like health, depends also on the deep involvement of those whose lives are at stake.  While efforts to improve vehicles, roadways, regulation, legislation, and law enforcement will continue to reduce harm from traffic crashes, the main opportunity for substantial reductions is through people taking steps to protect themselves from this large source of harm.  It will certainly not be easy to induce large numbers of people to stop doing things that are intrinsically enjoyable, such as high speed driving, high risk driving, and drunk driving.  Nor was it easy to induce people to abandon or moderate, to the extent that they have, such enjoyments as cigarettes, alcohol, the sedentary life, salt, sugar, and cholesterol-rich foods.  The considerable success in these health areas shows that it can be done, and offers an appropriate model for traffic safety.