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Collision avoidance systems will help save lives

03 October 2012

The second highest cause of automobile crashes is rear-end collisions. The solution, according to a professor of biomedical engineering at Virginia Tech is "slow the striking vehicle."

Clay Gabler (left) and his PhD student Kristofer Kusano
Clay Gabler (left) and his PhD student Kristofer Kusano

The concept is simple, even though the execution is complex and expensive. But in a life-and-death scenario, it is worth the investment, agree Clay Gabler, a professor of biomedical engineering at Virginia Tech, and Kristofer Kusano of Herndon, Virginia, a doctoral student in mechanical engineering. In affiliation with the Virginia Tech-Wake Forest Centre for Injury Biomechanics and the Virginia Tech Transportation Institute, they are conducting research on the potential benefit of a suite of collision avoidance systems now available as options on some new cars.

Their research, which has been published in peer-reviewed journals, predicts that the use of three systems may reduce serious injuries by as much as 50 percent (on a par with the use of seat belts).

Gabler and Kusano are looking at three systems that can operate independently or in sequence to prevent or mitigate a front collision. They have looked at one generic system that begins with a warning 1.7 seconds before a potential crash. Once alerted, if the driver begins to apply the brakes, there is brake assistance. "The car says, 'Let me show you how to do it more effectively and applies the necessary braking force'," said Gabler.

Finally, 0.45 seconds before the collision, the car will add 0.6 G to the braking effort, or if there is no braking, will apply the brakes autonomously.

"These systems require radar and sophisticated computers. So there is a lot of interest in determining how efficient they could be to guide development," said Kusano.

He and Gabler looked at collisions from the National Automotive Sampling System/Crashworthiness Data System for 1993 to 2008. US Department of Transportation crash teams look at about 5,000 crashes a year out of some 6 million police-reported crashes. Investigation includes photographing and making diagrams of the scene of the collision, collecting information from police and medical records, conducting interviews with the occupants, and measuring damage to the vehicles. To be investigated, crashes must involve at least one passenger vehicle, and at least one vehicle must have been towed from the scene due to damage.

The Virginia Tech researchers extracted 1,396 incidents of rear-end collisions from this database and looked at them on a case-by-case basis to determine whether the intelligent vehicle systems being studied would have been called into play and, if so, how they would have helped.

"Warning works in alerting a distracted driver so they apply the brakes," said Gabler. The study of the crashes determined that 71 percent of the drivers were braking and 29 percent were not. Simulations were run of the crashes, and then assisted or autonomous braking was simulated.

The research showed that 7.7 percent of crashes would be prevented by use of all three systems – warning, assisted braking, and autonomous braking. "We looked at one generic system with a 1.7 second warning. If the warning were sooner, it would prevent more crashes, but there would also be false alarms, which results in drivers turning the systems off or ignoring warnings," Gabler said.

Kusano and Gabler are also looking closely at driver behaviour. "Not accounting for driver behaviour may overestimate the potential target population for a safety system," said Gabler.

They used the National Motor Vehicle Crash Causation Survey. To be included in the survey, Emergency Medical Services must have been activated and an investigator must have been at the scene of the crash before it was cleared. This allowed investigators to interview occupants, witnesses, and first responders in order to determine factors which led to the crash -- details not available in traditional crash databases that focus on injury.

The Virginia Tech researchers examined the critical reason assigned by the crash investigator to each crash, then determined the behaviour that resulted in the most common type of fatal crashes, which are road-departures, and the most common type of all crashes, rear-end crashes.

For road departures, performance errors, such as poor directional control or over-compensation, were the most frequent critical reason for the crash for 23 percent of drivers. Distraction was the next most common critical reason for 22 percent; and non-performance errors, such as falling asleep or having a serious illness prior to the crash, was the most common critical reason for 21 percent of road departures. Speed-related critical reasons were cited in 19 percent of collisions.

The most frequent pre-crash scenario for rear-end collisions was driver distraction, accounting for 51 percent of such collisions.

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