WASHINGTON-The success of anti-lock brakes may come down to breaking old driving habits. According to two recently released studies, the performance of ABS has been variable. Researchers conclude many drivers might be using them incorrectly.
Drivers shouldn't pump anti-lock brakes, the opposite of what most drivers traditionally have been taught.
``We want to remind people that when they step on the brake, you want to push down hard and keep the pedal pushed down,'' said Dr. Ricardo Martinez, head of the National Highway Traffic Safety Administration, which released its ABS study Feb. 1.
He said NHTSA would suspend rulemaking on ABS in passenger cars and light trucks until it could learn more about how such systems operate in those vehicles.
The NHTSA report showed mixed results for ABS performance. Cars with such systems had a 24-percent decrease in multivehicle fatal crashes, compared with cars without ABS, and a 27- percent drop in pedestrian and bicycle fatalities involving cars.
Anti-lock brake systems are designed to prevent a vehicle's wheels from locking to give better control and decrease stopping distance during emergency braking.
When the anti-lock brakes engage, the driver won't hear the brakes squeal but will feel the pedal vibrating. That's because the system is working, pumping the brakes faster than humanly possible, Dr. Martinez said.
``But if you're not familiar with the system, you may think it's not working and take your foot off the pedal or turn to over correct.''
According to Charles Kahane, the mathematical statistician for the 150-page NHTSA study, there were 14 percent fewer nonfatal crashes among cars with anti-lock brakes on wet roads.
However, drivers with anti-lock brakes ran off the road, leading to a death inside the car, 28 percent more often in comparison with non-ABS vehicles, he said.
The reason for this is unclear, according to Dr. Martinez. ``We need to know whether this disturbing increase is a consequence of ABS, or is due to other causes.''
He believes drivers might be turning the wheel in anticipation of correcting skidding, which anti-lock brakes are designed to prevent.
``A driver hitting the anti-lock brakes only needs to turn enough to avoid hitting objects such as other cars,'' he said. ``The car will go in the direction the driver turns.''
NHTSA, the safety arm of the Department of Transportation, studied 4,000 fatal crashes from 1989-93 in the Fatal Accident Reporting System, which accumulates crash data. It also used records on 47,000 cars in accident reports from 1990-92 in Florida, Pennsylvania and Missouri.
A study released Feb. 2 by the Highway Loss Data Institute (HLDI), an organization funded by the insurance industry, was even less encouraging. It showed ABS neither reduces the frequency nor the cost of car accidents.
A claim was $2,375, on average, for each 1991 car without anti-lock brakes, and $2,469 for those with them. The frequency of claims was 7.5 percent in 1991 and 7.6 percent in 1992.
The institute study was based on a comparison of insurance claims between 693,057 General Motors Corp. cars with anti-lock brakes built in 1992 and 514,662 same-model GM cars without them built in 1991.
The insurance industry currently gives discounts to drivers whose cars have anti-lock brakes.
``(There's) nothing wrong with the (ABS) technology,'' said HLDI President Brian O'Neill. ``(But) the circumstances are rare in which anti-locks can help. Not as many crashes as people suppose are preceded by loss of control that anti-locks can prevent.''
While the HLDI's conclusions are more pessimistic than the government study, Mr. O'Neill agreed with Dr. Martinez about what might be driving the numbers.
``When it's wet, go somewhere off-road like a parking lot and practice hard braking so the anti-lock feature is engaged,'' Mr. O'Neill suggested. ``It's important to `unlearn' past braking habits.''
ABS does not necessarily shorten stopping distances, nor will it prevent skidding caused by non-braking maneuvers, such as going too fast around a curve.
Above all, both groups warned motorists to never pump anti-lock brakes-the system will engage only if the driver's foot is kept on the brake.
ABS is on about half of 1994 vehicles. The government does not require anti-lock brakes in cars.
Ms. O'Brien is an Associated Press writer. Miles Moore, TIRE BUSINESS' Washington correspondent, contributed to this report.