The Obama administration has said that it may require automakers to install “smart pedals” on all new cars. This kind of system — already used in BMWs, Chryslers, Volkswagens and some of the newest Toyotas — deactivates the car’s accelerator when the brake pedal is pressed so that the car can stop safely even if its throttle sticks open.
The idea is to prevent the kind of sudden acceleration that has recently led to the recall of millions of Toyotas. Federal safety regulators have received complaints asserting that this problem has caused accidents resulting in 52 deaths in Toyotas since 2000. Smart pedals might help prevent more such accidents if the cause of unintended acceleration turns out to be some vehicle defect.
But based on my experience in the 1980s helping investigate unintended acceleration in the Audi 5000, I suspect that smart pedals cannot solve the problem. The trouble, unbelievable as it may seem, is that sudden acceleration is very often caused by drivers who press the gas pedal when they intend to press the brake.
From the mid-1980s until 2000, thousands of incidents of sudden acceleration were reported in all makes and models of cars (and buses, tractors and golf carts). Then, as now, the incidents were relatively rare among car crashes generally, but they were nevertheless frequent and dangerous enough to upset automakers, drivers and the news media.
I looked into more than 150 cases of unintended acceleration in the 1980s, many of which became the subject of lawsuits against automakers. In those days, Audi, like Toyota today, received by far the most complaints. (I testified in court for Audi on many occasions. I have not worked for Toyota on unintended acceleration, though I did consult for the company seven years ago on another matter.)
In these cases, the problem typically happened when the driver first got into the car and started it. After turning on the ignition, the driver would intend to press lightly on the brake pedal while shifting from park to drive (or reverse), and suddenly the car would leap forward (or backward). Drivers said that continued pressing on the brake would not stop the car; it would keep going until it crashed. Drivers believed that something had gone wrong in the acceleration system, and that the brakes had failed.
But when engineers examined these vehicles post-crash, they found nothing that could account for what the drivers had reported. The trouble occurred in cars small and large, cheap and expensive, with and without cruise control or electronic engine controls, and with carburetors, fuel injection and even diesel engines. The only thing they had in common was an automatic transmission. An investigation by the National Highway Traffic Safety Administration found no electro-mechanical defects to explain the problem. Nor did similar government studies in Canada and Japan or any number of private studies.
In the Toyota situation today, some have suggested that unintended acceleration has been caused by floor mats or sticking throttles, but there is considerable doubt about these explanations, and the search for the smoking gun continues. One thought is that computerized engine management systems or electronic controls may be to blame. And so it is interesting to note that unintended acceleration in the 1980s happened before the arrival of drive-by-wire controls and computerized engine-management systems.
Back then, many of us who worked in fields like ergonomics, human performance and psychology suspected that these unintended-acceleration events might have a human component. We noticed that the complaints were far more frequent among older drivers (in a General Motors study, 60-to-70-year-olds had about six times the rate of complaints as 20-to-30-year-olds), drivers who had little experience with the specific car involved (parking-lot attendants, car-wash workers, rental-car patrons) and people of relatively short stature.
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.
Yet the automatic shift lock did not entirely do away with sudden acceleration incidents — as the Toyota problems illustrate. The fix now championed by the Obama administration could work in situations in which there is an actual vehicle defect. It would tell the car that if it receives signals to both accelerate and brake, the accelerator should go dead so that the brake alone will work.
But this smart-pedal system can be of no use if the driver is simply pressing the accelerator and not touching the brake. The unintended acceleration — and the crash — would still occur.
What the smart pedal may do, however, is finally give us a sense of whether sudden acceleration tends to stem from operator error. If the reports of acceleration continue (and the smart pedals work properly), then there will be nothing and no one left to blame but the driver.
Richard A. Schmidt, a professor emeritus of psychology at the University of California, Los Angeles. An earlier version of this article misstated the name of the National Highway Traffic Safety Administration.