Carl F. Thelin

Pushing the Wrong Pedal

            Way back in the 1980s a scandal alleged that the Audi 5000 sedan had a defect under the hood that caused the car to run away under its own power. Other cars occasionally exhibited the same alarming behavior. Usually, the driver would claim that after he (or she) started the engine and shifted into gear, the Audi took off quickly. It would not stop even when the driver pushed the brake pedal hard. Sometimes the car crashed into another car, sometimes it smashed into a building. The car had not developed much speed before the collision, so usually the driver was not hurt bad. The cars with the alleged defect all had an automatic transmission.

            As a Crash Scene Investigator (CxSI), I have an advantage: I previously was the Auto Safety Engineer for Consumer Reports. There, I test drove the Audi 5000 when it was new. I knew that this car had large wide tires to accommodate the powerful 5 cylinder engine. There is a bulge on the left side of the space for the brake and accelerator pedals. This displaced the pedals toward the center of the car more than on most automobiles because of the wide tires. Because of that lateral shift, it was easy to press on the accelerator pedal with the right side of your foot while also pressing on the brake pedal. It occurred to me that drivers, especially older drivers with degraded hearing, would start the car and place it in gear quickly, without hearing the engine revving much faster than idle. Then when the car took off, they pressed hard on the accelerator, thinking it was only the brake pedal.

            What do we know about other cars that had unexpected acceleration like this?  A CSxI who is working with a possible client has a demonstration to show that the problem was misplacement of the driver’s right foot. I could take almost any car with an automatic transmission to show how unlikely a real runaway would be. Even if the car had a powerful V-8 I would start the engine and shift into Drive normally. Then with my left foot on the brake pedal, we would mash the accelerator pedal. The driven tires might begin to spin and make blue smoke but the car would remain in place. All four wheels had locked brakes, but the engine was overpowering only two of them. The front brake and tires were very effective if we started that with the car not moving. If I attempted this demonstration when the car was going 60 mph, overcoming the inertia would be more difficult – maybe impossible.

            I could get a runaway under another scenario. If we pumped the brake pedal while the engine was revving hard, that would deplete the power-brake vacuum booster reservoir. Then the brake effect would be like having non-power brakes – requiring greatly increased pedal force to hold the car back. That was good reason to adopt another means of assuring that the brake booster is not dependent upon engine intake vacuum. Audi did that.

            We proved that the “ghost under the hood” was not real. Runaways were the result of careless drivers. True, the Audi made the error more likely with the weirdly placed pedals. None of this seemed to affect the adverse publicity generated by the TV show “60 Minutes”. The result was greatly reduced sales for Audi. Another result of this scandal was the adoption of the brake-shift interlock mechanism that made it necessary to depress the (real) brake pedal in order to get the gear shift out of Park.