Several researchers hypothesized how a driver, intending to apply the brake pedal to keep the car from creeping, would occasionally press the accelerator instead. Then, surprised that the car moved so much, he would try pressing harder. Of course, if his right foot was actually on the accelerator, the throttle would open and the car would move faster. This would then lead the driver to press the “brake” harder still, and to bring about even more acceleration. Eventually, the car would be at full throttle, until it crashed. The driver’s foot would be all the way to the floor, giving him the impression that the brakes had failed.

In the cases that went to court, jurors naturally asked, why would a driver with decades of driving experience suddenly mistake the accelerator for the brake? And why would the episode last so long  often 6 to 10 seconds or more? Wouldn’t that be ample time to shut off the ignition, shift to neutral or engage the parking brake?

First, in these situations, the driver does not really confuse the accelerator and the brake. Rather, the limbs do not do exactly what the brain tells them to. Noisy neuromuscular processes intervene to make the action slightly different from the one intended. The driver intends to press the brake, but once in a while these neuromuscular processes cause the foot to deviate from the intended trajectory  just as a basketball player who makes 90 percent of his free throws sometimes misses the hoop. This effect would be enhanced by the driver being slightly misaligned in the seat when he first gets in the car.

The answer to the second question is that, when a car accelerates unexpectedly, the driver often panics, and just presses the brake harder and harder. Drivers typically do not shut off the ignition, shift to neutral or apply the parking brake.

In 1989, the National Highway Traffic Safety Administration concluded that the incidents of unintended acceleration by the Audi 5000 were mostly caused by this kind of pedal error  not some electro-mechanical defect in the vehicle. To fix the problem, Audi designed something called an automatic shift lock, which, when the car is being started, keeps the transmission in park unless and until the brake pedal is depressed. If the driver should press the accelerator instead of the brake, the vehicle remains safely in park.

(In a car with a manual transmission, a driver is naturally prevented from making a simple pedal error, because even if his right foot goes to the accelerator instead of the brake, the car still will not move unless he also intentionally lifts his left foot from the clutch.)

Audi ultimately gave the world’s other automakers the rights to the patent on the automatic shift lock and by the mid-1990s virtually all new cars had adopted the feature or some variant of it. Incidents of sudden acceleration when people started their cars dropped sharply. The shift lock not only made people safer but also provided evidence for the hypothesis that most of the problems had been caused by driver error.