Unintended Acceleration : Three Ways to Stop!

How to Deal With Unintended Acceleration - Car and Driver -

BY DAVE VANDERWERP
December 2009

Our tests were conducted at highway speeds, as the incident with the Lexus ES350 happened on an expressway, and in the lowest possible gear, as that's the worst-case scenario. Here is how to deal with a runaway car:

*Hit the Brakes*

Certainly the most natural reaction to a stuck-throttle emergency is to stomp on the brake pedal, possibly with both feet. And despite dramatic horsepower increases since /C/D/’s 1987 unintended-acceleration test of an Audi 5000, brakes by and large can still overpower and rein in an engine roaring under full throttle. With the Camry’s throttle pinned while going 70 mph, the brakes easily overcame all 268 horsepower straining against them and stopped the car in 190 feet—that’s a foot shorter than the performance of a Ford Taurus /without/ any gas-pedal problems and just 16 feet longer than with the Camry’s throttle closed. From 100 mph, the stopping-distance differential was 88 feet—noticeable to be sure, but the car still slowed enthusiastically enough to impart a feeling of confidence.

We also tried one go-for-broke run at 120 mph, and, even then, the car quickly decelerated to about 10 mph before the brakes got excessively hot and the car refused to decelerate any further. So even in the most extreme case, it should be possible to get a car’s speed down to a point where a resulting accident should be a low-speed and relatively minor event.

But Toyota could do better. Since the advent of electronic throttle control, many automakers have added software to program the throttle to close—and therefore cut power—when the brakes are applied. Cars from BMW, Chrysler, Nissan/Infiniti, Porsche, and Volkswagen/Audi have this feature, and that’s precisely why the G37 aced this test. Even with the throttle floored and the vehicle accelerating briskly, stabbing the brakes causes the engine’s power to fade almost immediately, and as a result, the Infiniti stops in a hurry. From speeds of 70 or even 100 mph, the difference in braking results between having a pinned throttle or not was fewer than 10 feet, which isn’t discernible to the average driver.

As a result of the unintended-acceleration investigation, Toyota is adding this feature posthaste.We included the powerful Roush Mustang to test—in the extreme—the theory that “brakes are stronger than the engine.” From 70 mph, the Roush’s brakes were still resolutely king even though a pinned throttle added 80 feet to its stopping distance. However, from 100 mph, it wasn’t clear from behind the wheel that the Mustang was going to stop. But after 903 feet—almost three times longer than normal—the 540-hp supercharged Roush finally did succumb, chugging to a stop in a puff of brake smoke.

*Shift to Neutral or Park*

This is your best option in an emergency. Neither the Camry’s nor the Infiniti’s automatic transmission showed any hesitancy to shift into neutral or park when accelerating at full tilt. (Automatics have a piece of hardware called a park pawl, which prevents the transmission from actually engaging park and locking the wheels at speed—it creates a disturbing grinding sound, but the car essentially coasts freely.) The Roush had a manual, so you’d simply depress the clutch. In either case, power is effectively kept from the wheels and the car will be able to brake with its usual undiminished vigor, engine racing or not.

*Turn It Off*

Switching off the ignition is a sure way to silence an engine, but it’s probably the least desirable action because it will also make the car more difficult to maneuver. It causes a loss of power-steering assist, plus it will cut off vacuum boost for the brakes. The new wrinkle here: the keyless, push-button start-and-stop systems in many vehicles. Owners need to be aware that these systems require a long press of the button to shut off power when the car is moving (so that an inadvertent touch of the button by the driver doesn’t kill the engine).

Here, too, the Toyota was slightly behind the curve; the Infiniti’s engine shut down after a 2.5-second press of the button versus 3.3 seconds for the Camry. In an emergency, that would probably feel like an eternity. For some perspective, if a V-6 Camry’s throttle became stuck at 60 mph, the car would accelerate to nearly 80 mph before the engine would surrender. Furthermore, short, frantic pressing of the Toyota’s start/stop button—the probable response in an emergency—does nothing, whereas the Infiniti kills the engine after three rapid-fire presses.

*Conclusion*

In the end, though, we found no major deficiencies with the Camry’s ability to defuse an unintended-acceleration situation. But the No. 1 automaker could learn a few lessons from the competition here—namely a throttle cutoff and a more responsive push-button ignition.