Book Review Traffic Safety

Title: Traffic Safety
Author: Leonard Evans
Publisher: Science Serving Society, Bloomfield Michigan, USA
Other details: 445 p. Price: $ 99.50

In this admirable monograph, our immediate -past president Leonard Evans presents his vision for a safer traffic system. He eloquently argues that current safety policy of many countries, the USA prominently among them, dramatically fails. Each year hundred thousands of lives and billions of dollars are spilled, and millions of severe injuries are needlessly sustained, many leading to life long disabilities. He further argues that modest changes to a number of components of the traffic safety system currently in place can, in combination, lead to major reductions in harm.

According to him the key to progress is a different relationship between those at risk and the institutions in place to protect them. The goal of traffic law is not to apprehend and punish violations, but to reduce harm by preventing violations. A breakthrough in road traffic safety can be achieved by adopting the same two central principles that led to such outstanding safety in commercial air travel. First, the primary goal must be to prevent crashes, not to make it safer to crash. Second, drivers must follow rules based on inputs from many professional disciplines, rather than relying mainly on what they have learned from their personal experience. A central idea is that public support for electronically monitoring and enforcing driver behaviour should be increased and this could be reached by making the public aware of the high extent to which risk in traffic is due to other drivers.

Evans bases his conclusions on a thorough statistical analysis of the safety effects and costs/benefits of technical safety measures like airbags, which he discusses very critically, and on an analysis of human factors in traffic performance and traffic behaviour, like effects of age and gender. With regard to technical constructions to reduce the effect of a crash, he argues that only limited additional safety value at relatively excessive financial costs, can be obtained beyond the massive positive effects already obtained by the safety belt and vehicle design changes over the decades.

To illustrate this point he shows that “a belted driver in a modern car is less than half as likely to die as a driver in a 1950 car of similar mass in an identical crash (p, 415)” . He further shows that the airbag has yielded only little additional safety in comparison to that, and it did so at a (too) high financial cost. As he is convinced by his analyses and observations that the two factors that overwhelmingly determine an individual’s risk in traffic are the individual’s behaviour and the behaviour of other road users, he thinks the focus must now be on traffic behaviour and he argues that in this area large improvements in traffic safety can be obtained at acceptable costs, using new technological developments in the domain of driver monitoring and traffic law enforcement.

Most importantly, however, policy changes in designing and enforcing traffic safety measures would be required starting from the view that traffic unsafety is a major public health problem which government has an obligation to address. An already implicitly accepted principle must be even more openly embraced, namely that driving is a public, not a a private activity, weakening privacy arguments to oppose using technology to better enforce traffic law. Evans realizes, however, that such measures can only be effective if the public accepts them, so the public must be convinced that traffic law enforcement is not just another revenue-raising scheme.

Each individual chapter of this higly readable and important book will now be briefly mentioned, summarizing its major conclusions.

In chapter 1 (introduction) the magnitude of the world’s traffic unsafety problem is drawn and the superiority of crash prevention over crashworthiness interventions is argued. “This is because crashworthiness measures typically convert fatalities into serious injuries, whereas when the crash is prevented , all harm from it is prevented (p. 17)”. Also he introduces the rates and statisticall background used to describe traffic unsafety and shows that ” different rates address different questions – no one rate is superior to others in any general sense”.

In chapter 2 (data sources) properties of data sets that are essential to derive the quantitative results central to scientific understanding are introduced. A very importantant data set is the Fatality Analysis Reporting System (FARS), a census of all fatal crashes on US public roads since 1 January 1975 (now above 1.000.000 fatalities). Also various injury classification systems are discussed but it seems that their reliability is less than for fatalities, also depending on financial aspects of the medical care system.

In chapter 3 ( overview of traffic fatalities) it is shown how as countries motorize, traffic fatalities per year initially increase steeply to maximum and then decline. Also it is shown how the higher the motorization, the lower are the fatalities per registered vehicle. Male fatalities outnumber female ones by more than a factor of 2. Even for non-drivers, such as pedestrians and passengers, male fatalities outnumber female. Most vehicle occupants are killed in single vehicle crashes, rollover being the most harmful event. Safety belt use by occupants killed in rollover crashes -often ejected from the vehicle- is very low on average. Remaining in the vehicle, accomplished by properly wearing a safety belt, reduces risk by about 80 %.

In chapter 4 (vehicle mass and size) Newtonian mechanics is applied to predict how the weight and size of cars influence fatality risk. Confronting the equations with the FARS data it can be shown that for two-vehicle crashes, if one car is twice as heavy as the other, the driver in the lighter car is 12 times as likely to die as the driver in the heavier car. Size also matters: “A car can be made lighter while at the same time safer to the occupants and to the occupants of other vehicles into which it crashes by increasing its length (p. 95)”. SUV’s are discussed also; their weigth may be a positive safety feature, at least for who is inside, but their higher rollover opportunity is a negative feature.

In chapter 5 (environment, roadway and vehicle) many prejudices about safety and unsafety are tripped up. It is shown that statistically –in terms of fatalitities per distance- it is actually safter to drive in winter on snowy roads than in summer on dry roads. Also it is shown that in terms of fatalities the safety effect of ABS is not positive. It is true that it reduces crashes on wet roadways becuase it prevents skidding but it appears that rollover risk increases. The underlying explanation presented is speed; snow reduces travel speed leading to greater safety and the superior braking performance with ABS encourages small increases in speed. Also the application of modern –European style – roundabouts is promoted in the chapter, again because they reduce speed and because they “essentially eliminate the most severe type of intersection crash- one vehicle striking another on the side”.

In chapter 6 (gender, age and alcohol effects on survival) it is shown that these three factors have large effects on the physical vulnerability (fragility) of the body, as defined in terms of fatality risks, given the same impact. Young adullt males who have used no alcohol are most “robust”. Seventy year old males have about 3.5 times greater fatality risks than 20 year old males. Adult females are more fragile than males by a factor of about 1.3 but before age 15 and after age 50 there is no gender difference. Children are more vulnerable than young adults. Also, given the same impact, drivers with higher blood alcohol concentration are substantially more vulnerable. In all these cases other causes of the different fatalty risks have been neatly controlled, most importantly by the use of the famous “double pair comparison-method”.

In chapter 7 (older drivers) an interesting distinction is made between risks to the drivers themselves and threats they pose to other road users. In one of the tables based on FARS data on pedestrians killed by impact from a car, Evans shows that, on average, licensing an 80 year old poses a 70 % less threat than licencing a 20 years old. Risks older driver themselves face are mostly determined by increased physical vulnerability, although in the age range from 75 and up there is evidence of increasing fatalty risks over and above the vulnerability effect caused by decresing performance levels. Evans does not advocate to base licencing decisons on high age. Because of the large individual differences, he advocates tests that apply to all without regard to age. He finishes the chapter as follows (p. 172): “Young male drivers have the highest fatality and crash rates, and pose the greatest risk to other road users. A central finding of traffic safety in every country in the world is that traffic crashes are overwhelmingly a problem of young male drivers”.

In chapter 8 (driver performance) the knowledge, skill and perceptual and cognive abilities of drivers are discussed. In a computational example on reaction time and braking, Evans shows that small reductions in reaction time can produce large reductions in the probability of crashes which he then applies to understand the positive effects of the high-mounted stop lamps. He also critically discusses driving simulators, His central argument is that driving simulators are unlikely to produce knowledge relevant to traffic safety becuae they measure driver performance”what a driver can do” and not driving behaviour “what the driver in fact chooses to do”. The latter factor, however. primarily determines traffic unsafety. In my view this argument most clearly applies to the “healthy younger driver unsafety problem but less to the use of simulators in training and assesment of functionally impaired drivers who may have a safety problem on the level of skills and abilities. With regard to the healhy young driver he illustrates that the basic skills required to start, stop, and steer are acquired remarkably easily and quickly. Nevertheless risk taking behaviours associated with youth, and lack of higher level driving skills contribute to a 10 times higher crash risks in teenagers beinning to drive than in 40-50 years old drivers. He proposes extending and refining graduated licensing as a major contribution to traffic safety.

In chapter 9 (driver behaviour) a central element of driver behaviour is focused, namely chosing travel speed. Ïncreasing speed increases the risk of crashing, of being injured and of being killed. A one percent increase in speed increases fatality risk by between 4 and 12 %. From relating data on crimes, testosterone level, gender and crash involvement, Evans comes to the conclusion that the high crash rates for male and young drivers reflect inherent immutable biological characteristics and he thinks it is not wise for traffic safety policy to try to change these characteristics. Rather it mist be tried to reduce risks for everyone.

In chapter 10 (alcohol) the effect of large dosed of alcohol on fatality risk are explained from riskier manoeuvres (behaviour), impaired skills (performance) and incresed physical vulnerability, in that order. The dubious role of the alcohol industry is discussed. Leonard Evans thinks that large reductions in US traffic deaths can be achieved by expanding the use of sobriety check lanes, increasing taxes on alcohol, especially beer, and prohibiting beer advertising on television. He is rather positive about “alcohol ignition interlock systems” but discusses them as devices for repeat offenders only, who are only a small minority of all offenders. Reading the book as a whole, makes one wonder, however, why this device is not made obligatory for any car driven by 16-24 years old drivers, rather than obliging potentially confidence- and speed-raising technology like ABS and airbags.

In chapter 11 (occupant protection) the effects of protection devices on fatalities are assessed and discussed. The safety belt and the motorcycle helmets are unprecedented successes, having reduced driver fatality risk in a crash by 42 %. and 28 % respectively. Since drivers who do not spontaneously use safety belts differ from natural bucklers in the sense that they tend drive more risky anyway, getting the former ones into the belts would lead to large reduction of fatalities. This should provide “increased motivation to pass stronger belt wearing laws and enforce them vigorously (p. 305)”.

In chapter 12 (airbag benefits, airbag costs) the (US) policy and the safety evidence with regard to airbags are skillfully filleted and the airbag is shown to be very expensive fish with only faint taste and nasty fishbones. In this chapter and in in chapter 15 the US policy with regard to pushing the airbag and the role of the NHTSA are very criticallly discussed.

In chapter 13 (measures to improve traffic safety) a systems framework is used to sort out the independent and interactive effects of road user factors (driver behaviour and driving performance) and engineering factors, namely characteristics of the infrastructure (traffic and roadway) and the vehicle (automotive). According to him, engineering factors have only accounted for a small proportion of the enormous decline in fatalities per vehicle since the beginning of motorization and for the large differences in traffic unsafety between countries. Evans argues that the countermeasures that have produced the largest change in behaviour, and consequently largest reductions in traffic harm, are all legislative and continuing on this track he promotes more effective enforcement of traffic law, particularly with regard to speeding and not using seat belts, as the most effective approaches to improve traffic safety. Another interesting feature of the chapter is the comparison between the safety characteristics of commercial air carriers and road transportation. In airline travel the number one priority is on avoiding the crash rather than marginally increase the probability of surviving it. ” When road safety transfers its main focus to the prevention, rather than the survival, of crashes, it can start moving in the direction of the extraordinary safety achieved in airline travel (p. 355)”.

In chapter 14 (how you can reduce your risk) Evans gives sometimes very personal suggestions about (not) getting involved in at-fault and not-at-fault crashes, including flashing brake light to deter tailgaters (altruistically he warns against doing that if the tailgater is also being tailgated). He also advises not to drive a company car and not to take insurance for coverage of repair and replacement of your own vehicle, refering to Milton Friedman’s famous oneliner “Nobody spends somebody else’s money as carefully as he spends his own”.

In chapter 15 (the dramatic failure of US safety policy) he exposes a negative side of a legislative approach to traffic safety, particularly the one sided US focus on technological changes to the crashworthiness of cars, independent of driver behaviour, encouraging people’s ideas that deaths in traffic are mainly due to unsafe and defective vehicles. He also blames the NHTSA and the media for their dubious roles. “The media did not mention that these factors had only little to do with the overwhelming majority of the 40.000 annual US deaths. The crucial factors over which driver do have control, wearing belts, alcohol, speeding…were deemphasized. Yet these are the factors that have massive effects on safety (p. 408)”.

In chapter 16 (Vision for a safer tomorrow) Leonard Evans sketches his program for improving road safety. A central idea is that public support for enforcing traffic law should be increased and this could be reached if public awareness of the high extent to which risk in traffic is due to other drivers. In 69 % of the US fatalities in a given year a driver other than the person killed was involved and for less motorized countries this percentage is even larger. “A major adavance in safety will occur if the public realizes that more effective monitoring of other drivers (with regard to speeding and belt use) provides them far more protection than searching luggage (for bombs and guns on airports) (p. 414)”. With regard to the question what should be done with fines, he categorically opposes using them for nonspecific governement funding and he suggests they should be kept in a separate account, at the end of the year divided equally among all licence holders.