What a joy to be asked to review a book on traffic safety! The last book I reviewed for a medical journal was on bioterrorism. Like most doctors, I know almost nothing about bioterrorism, which, despite the current hype, remains a fairly trivial public-health issue. I suspect the reason I was asked to review a book on bioterrorism was that I had recently published a short article on the increasing number of editorials and papers about bioterrorism published in the five major medical journals (Annals of Internal Medicine, BMJ, JAMA, The Lancet, NEJM) in the run-up to the war in Iraq. To provide a yardstick against which to assess the attention given to bioterrorism, I also counted the number of articles published on traffic accidents, which kill about 3000 people worldwide every day, and which is a topic that I do know something about. There were twice as many articles on bioterrorism.

The threat of bioterrorism serves an important political function. It allows governments, which mainly represent the interests of the ruling classes, to terrorise the domestic population, to restrict civil liberties, and to justify spending huge amounts of taxpayer's money on armaments. The threat of traffic accidents, on the other hand, serves no useful political function. According to Leonard Evans in Traffic Safety, if governments enforced traffic safety laws, which should include the use of automatic detection technology, injury rates could be halved. But in enforcing such laws, governments run the risk of falling out of favour with the ruling classes. Cars are built for speed and power, and even if they do spend most of their working lives idling in gridlock, the fantasy alone sells cars and makes money.

If you want to understand why enforcing the traffic safety laws will save lives then read Traffic Safety. Evans holds a degree in physics and was principal research scientist with General Motors for over 30 years. He uses data from the US Fatality Analysis Reporting System to show that Newton's laws of motion also apply on the roads (well at least in the USA). Speed is critically important. Speed provides the kinetic energy that twists metal and tears flesh. Indeed, one of the largest reductions in US road death rates was when speed limits were reduced in response to the 1973 oil embargo. Sadly, over the next 20 years, as the crisis faded into the past, the speed limits were raised again.

Nor was this the only link between geopolitics and road deaths. In an excellent chapter on vehicle mass and fatality risk, Evans explains how high oil prices in the USA in the early 1970s resulted in the introduction of the Corporate Average Fuel Economy (CAFE) programme in an attempt to encourage fuel conservation. CAFE required manufacturers to meet fuel economy targets in all new vehicles. But fuel use is directly related to mass, so CAFE resulted in lighter vehicles. In single-vehicle road-traffic crashes, which account for 49% of occupant deaths in the USA, heavier cars have a lower fatality risk. According to Evans, the introduction of CAFE thus led to thousands of additional road deaths.

But what about the pedestrians and cyclists who account for the majority of the victims of road-traffic crashes worldwide? Do the laws of physics also apply to them? Picture this: two obese stockbrokers jogging around New York's Central Park. They are on a collision course and unable to avoid a crash. There is much groaning, but no injury. Their energy-absorbing abdomens allowed for a relatively gradual rate of change of momentum. They dust themselves down, share some pleasantries, and congratulate each other on how their large size and mass have protected them. So, yes--the laws of physics apply to pedestrians. But apart from a passing reference to the fact that a heavy car will do more damage to a pedestrian than a lighter car, and his important suggestion that when a vehicle strikes a pedestrian the driver should be presumed to be at fault rather than the pedestrian--Evans rarely mentions pedestrians and cyclists, which is a serious oversight.

For over 3·5 million years, people have roamed our beautiful planet on foot. A child's first faltering steps are invariably greeted with delight because walking represents a key developmental milestone--just as it was a milestone in the evolution of human life. Walking is part of our humanity. How can a book on traffic safety overlook the fact that where there are no cars there is no risk? The most radical prevention strategy is to tackle the problem at source, with transport and land-use policies that reduce car use. Building clustered, high-density communities with nearby amenities would reduce the need for car travel. Encouraging safer modes of transport--improved mass transit, train, and bus services for longer journeys and walking and cycling for shorter ones--could slash road deaths. Such policies would also raise physical activity levels and thus help to tackle the global epidemic of obesity. They would reduce our dependence on fossil fuels, reduce global warming, and perhaps even prevent oil wars like the one raging in Iraq.

Readers of Traffic Safety will note that Evans is President of Science Serving Society, an organisation "devoted to adding reason and knowledge to public policy". Science should, of course, be at the service of society, but we should not be seduced into thinking that science is a neutral, value-free endeavour that can only help to set society on the right track. This book shows clearly why this is not the case. Evans is a brilliant scientist whose work deserves to be read, but this is a book on traffic safety written by someone steeped in the values of General Motors for most of his working life--and raised in a country where most people have at least one car and where walking has become an aberration. Contrast Evans' vision for a safer tomorrow--better methods for preventing crashes and automatic detection technology--with that of Enrique Peñalosa, the Mayor of Bogotá, Colombia. In a 2002 interview entitled The Politics of Happiness published in Land and People, Peñalosa described the ideas that helped him radically transform Bogotá in only 3 years.

"We really have to admit that over the past 100 years we have been building cities much more for mobility than for people's well-being. Every year thousands of children are killed by cars. Isn't it time that we build cities that are more child friendly? . . . One common measure of how clean a mountain stream is [is] to look for trout. If you find the trout, the habitat is healthy. It is the same way with children in a city. Children are a kind of indicator species. If we can build a successful city for children, we will have a successful city for all people."