Government study confirms ABS effectiveness, but mysteries linger

Consumer Reports News: August 28, 2009 11:22 AM

A just-released study from the National Highway Traffic Safety Administration (NHTSA) finds that antilock brakes (ABS) significantly reduce crashes where people get injured but have no net effect on crashes where people die. ( Download pdf.) That’s a big step forward from earlier government studies, which found that fatalities actually increased in cars with antilock brakes. The new study looked at 11 years worth of data, making the sample sizes much larger than in previous efforts.
 
The key finding:
“ABS by itself has close to zero overall effect on fatal crashes, but significantly reduces nonfatal crash involvements by an estimated 6 percent in cars and 8 percent in LTVs [light-truck vehicles such as SUVs and pickups].  Fatal run-off-road crashes do increase significantly with ABS, but now by only 9 percent, rather than the initial 28 percent [reported in an earlier study], as the public has learned how to use ABS correctly. That 9 percent increase is offset by reductions with ABS of other types of fatal crashes – and more importantly, it will be far outweighed by the great anticipated benefits of ESC [electronic stability control].”
 
The fact that ABS-equipped cars reduce the number of crashes resulting in serious injury is good news. While it remains something of a mystery why ABS is over-involved in run-off—the-road fatal accidents, the incidence of that type of crash is expected to plummet as electronic stability control becomes more universal. Already widespread, ESC will be on every car by the 2012 model year. It happens that antilock brakes are a necessary component of a stability control system, so we wouldn’t have ESC unless we already had ABS. ( Learn more about ESC.)
   
Nobody has satisfactorily explained why, in the subset of fatal crashes that involves a car running off the road, those with antilock brakes fare worse overall than those without them. Pretty much everybody agrees, and we have demonstrated countless times in our brake tests, that ABS makes for shorter, straighter, more controllable stops, on both wet and dry pavement. One possible explanation is that since ABS lets you steer a car in a panic stop rather than just sliding into whatever you’re braking for, that it’s then possible to steer off the road and get into even more trouble, say by rolling over or side-swiping a tree.
 
Another possibility is that some people are still unused to the groaning and pedal-chugging that happens when ABS activates. Such people might then let off the brake too soon, and thus have a higher-speed, more lethal crash than otherwise.
 
Some have speculated that ABS, like four-wheel drive, breeds a false sense of security in some people, who then drive less cautiously than conditions permit.

The number of car occupants killed every year has been dropping steadily, and recent fatality rates are the lowest ever. We would expect that whatever the number of off-road fatalities was in the years covered by this government study, that number will get steadily lower from now on. That’s because the number of cars equipped with antilock brakes that do not also have stability control is going to diminish every year regardless of any other factor.  

Learn more about car safety.

 —Gordon Hard


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