This manoeuvre, known as the pursuit-intervention technique, or PIT, was developed in California in the 1970s. It has dangerous repercussions, according to Eddie Wren, a former traffic-control police officer in Britain. Injuries are common. And spun cars, unless rapidly boxed in by patrol vehicles, can take off again.
In the view of many experts, however, the PIT manoeuvre is becoming less effective as new traction-control systems are more widely deployed on cars. At the same time, run-flat tyres are making another common method of stopping a vehiclea strip of spikes dragged across its pathless certain to bring it to a halt. Even cars with standard tyres are not always incapacitated by the spikes. Some career along on their wheel-rims at up to 160 kph, says Geoffrey Alpert, an expert in vehicle-pursuit litigation at the University of South Carolina, in Columbia. The result is a lot of desparate high-speed chases, of which one in four result in someone getting injured, and which kill about 400 people a year in America alone. There is also a certain amount of accidental kidnapping, because thieves sometimes take vehicles from self-service petrol stations, while the driver is paying, without checking the back seat for children.
One way to avoid the need for chases would be to track felonious vehicles electronically, instead of running after them. StarChase, a company based in Virginia, has developed a way to do just that. A pneumatic cannon is mounted on the pursuit car. With the help of a guiding laser, it shoots a satellite-based tracking device smothered in epoxy goo on to the back of the vehicle it is after. That allows the police to fall back and track the suspect without endangering the public.
From the polices point of view, however, it would be better if they could actually stop a runaway car by satellite, not just track it. General Motors plans to allow them to do just that. From September its OnStar service, which provides navigation and emergency services to drivers, will include a system called Stolen Vehicle Slowdown. Police, who believe a car to be stolen, can ask an OnStar operator to disable its accelerator while leaving the steering and brakes in working order. Some people have concerns about technology that allows moving cars to be shut down, not least the worry that hackers might take over the system.
Military systems could also find a civilian role. Ron Madrid, an expert on non-lethal warfare, says that a new laser-warning system has proved particularly effective in reducing casualties at checkpoints in Afghanistan and Iraq. The device, known as an optical distractor, floods the windscreen of a vehicle with a blinding green light. The optical distractor is often coupled with low-frequency loudspeakers that are able to project verbal instructions to halt into noisy vehicles from a distance of more than 100 metres. Non-toxic, slippery chemical slops, designed to prevent the wheels of a vehicle getting traction, are also in development. Spiked nets, which can be laid flat on roads, entangle wheels.
According to Andy Mazzara, the director of the Institute for Non-Lethal Defence Technologies at Pennsylvania State University, prototypes of such devices employ a laser to create an ionised channel of air through which the blasters can direct an electromagnetic pulse. That pulse is capable of burning out the electronics in a car, including its engine-management system, without harming the occupants. Its deployment is still a few years away, largely because such blasters need to be able to emit different frequencies to knock out a variety of models. But when they come, runaway drivers will get a zapping they will never forget.
The Economist Newspaper Limited 2008