How to stop a runaway car: Don't pump the brakes

Consumer Reports News: November 04, 2009 12:56 PM

Despite a massive recall by Toyota of 3.8 million vehicles to address sudden runaway acceleration, National Highway Traffic Safety Administration (NHTSA) is still investigating the exact cause of this problem. They are concerned that the accelerator pedal getting stuck by the floor mat – the purpose of the recall - is not the exclusive cause, according to the New York Times.

Whatever the cause of unintended acceleration, the best defense is to know how to safely regain control of the car should it happen to you. In a previous post, we wrote that putting a car in Neutral might save your life. Our latest tests show that pumping the brakes at full throttle can make a bad problem even worse, as demonstrated this video from ABC News. (See the report "Owners of Toyota cars in rebellion over series of accidents caused by sudden acceleration" at ABCNews.com.)

A NHTSA report released this week points out that some drivers can "react by applying the brake pedal multiple times, depleting the braking system's (vacuum based) power assist.

Testing theory at the track
We decided to find out just how quickly you could lose power brakes with a stuck throttle. Using our test track and several test vehicles, we accelerated to 60 mph and hit the brakes with the accelerator still floored. Once the brakes were applied, the vehicles began fighting us. The transmissions downshifted trying to maintain speed.

Instead of holding the brakes, we tried pumping them. This test confirmed that pumping the brakes is a really bad strategy. Power brakes rely on engine vacuum to provide additional brake pressure. At full throttle, the engine doesn't generate any vacuum. So as soon as we removed and reapplied pressure to the brake pedal, the power assist disappeared and stopping the car became hopeless. "There was no way I could push hard enough on the brakes to slow the car down when the engine was fighting me," said Sr. Automotive Engineer Jake Fisher.

Bottom line
The best strategy to stop a runaway car is to press and hold the brakes and shift into neutral. Modern cars have rev limiters, which will protect the engine from over-revving. Even if your car doesn't, don't worry about your engine's life—worry about your own.

—Eric Evarts

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How to stop a runaway car: Don't pump the brakes

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