An examination of sudden acceleration

Pollard, John K.; Sussman, E. Donald · 1989 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This 1989 report by the Transportation Systems Center (TSC), prepared for the National Highway Traffic Safety Administration (NHTSA), investigates the causes of "Sudden Acceleration Incidents" (SAI). SAI are defined as unintended, high-power accelerations from a stationary or low-speed position, accompanied by an apparent loss of braking effectiveness. The study aimed to resolve public controversy regarding these incidents by evaluating potential mechanical, electronic, and human-factor causes. The research focused on ten vehicle models with above-average SAI complaint rates, including the Audi 5000, Buick LeSabre, and Toyota Cressida. The methodology involved convening a panel of independent experts, reviewing extensive literature and case documentation, interviewing involved drivers, and conducting rigorous engineering tests. TSC examined fuel systems, braking systems, and driving controls. Specific tests were performed at NHTSA’s Vehicle Research and Test Center (VRTC) to simulate fault conditions, including cruise-control malfunctions, idle-stabilizer failures, and electromagnetic interference. The study also analyzed pedal geometry and force-deflection characteristics to assess the likelihood of pedal misapplication. The findings indicate that no vehicle malfunctions were identified that could cause high engine power without the throttle being opened. While mechanical issues like stuck throttles or broken linkages could cause unintended acceleration, these failures are readily detectable in post-incident investigations. Electronic faults, such as those in idle-stabilizer systems, produced only modest acceleration increases (less than 0.3 g) insufficient to cause an SAI, though they might startle a driver into a pedal error. Cruise-control failures were found to be incapable of causing SAI in most modern vehicles due to redundant fail-safe designs; even in older analog systems, simultaneous failures required for undetectable throttle opening were deemed virtually impossible. Furthermore, actual brake system failure was ruled out as a significant factor, as physical evidence of brake failure was rare in reported cases. The study concludes that pedal misapplication is the most probable explanation for the vast majority of SAI cases where no vehicle malfunction is evident. Certain pedal design features—such as close lateral placement, similar force-displacement attributes, and vertical offsets that allow engine torque to exceed brake torque when both pedals are depressed—were found to increase the probability of such errors. All vehicles with high SAI complaint rates possessed these conducive pedal designs. The report recommends design changes to reduce misapplications, including moving pedals further apart, raising the brake pedal relative to the accelerator, and installing automatic shift-locks that require brake application before shifting out of park. These measures are expected to reduce the frequency of SAI without adverse safety consequences.

Key finding

Pedal misapplication is the most probable cause of sudden acceleration incidents, with vehicle design features such as close lateral pedal placement and similar force-deflection characteristics increasing the likelihood of this error.

Methodology

mixed_methods

Sample size: 10

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• pedal misapplication
• braking response