According to the U.S. National Highway Traffic Safety Administration, there were 5.4 million automobile crashes on U.S. roads in 2010, killing 33 000 people and injuring more than 2.2 million. In a paper recently published in IEEE Transactions on Intelligent Transportation Systems, two researchers at Virginia Tech’s Center for Injury Biomechanics delve into just how much of an effect systems that warn a driver about an impending front collision—then slam on the brakes if the driver doesn’t act quickly enough—might have on these crash statistics.
Automakers are starting to introduce vehicles equipped with electronic safety systems whose purpose is to keep cars from crashing. The researchers, Clay Gabler, a professor of biomedical engineering, and Ph.D. student Kristofer Kusano, studied a suite of systems that rely on radar to tell the car when it is coming dangerously close to another vehicle’s rear bumper. Some of these systems deliver an audible warning when the distance between the car and the one ahead of it gets too narrow.
Others offer braking assistance if the driver responds to the warning by applying the brakes. Still another type attempts to bring the car to a halt with a huge braking force if the driver has not hit the brake pedal 0.45 seconds before the sensors predict that there will be contact.
Gabler and Kusano combed through 5000 investigator reports of crashes. In computer simulations that recreated the scenarios of 1400 rear-end collisions (for which investigators from the U.S. Department of Transportation had gathered information such as photographs and diagrams of the crash scenes, police, driver, and occupant statements, and vehicle damage assessments), the Virginia Tech researchers were able to demonstrate the extent to which the electronics would have helped. They concluded that in most cases, the electronic safety systems would slow cars down enough to cut the number of serious injuries in half. Better still, they say, 7.7 percent of rear-end collisions would be avoided altogether.
“Even if the driver is distracted and does nothing, a system of this type would brake forcefully enough during that final half second before impact to slow a car traveling at [72 kilometers per hour] by about [10 to 12 km/h],” says Clay Gabler, who is also assistant director of the Center for Injury Biomechanics. “That might not seem like a lot,” he says, “but the aim is to reduce the energy of a collision. And since kinetic energy is related to the square of velocity, this change in speed reduces the likelihood of serious injury by about 35 percent. That’s huge.”