Sudden unintended acceleration (SUA) is the unintended, unexpected, uncontrolled acceleration of a vehicle, often accompanied by an apparent loss of braking effectiveness. It may be caused by some combination of driver error (such as pedal misapplication), or mechanical or electrical problems. The US National Highway Traffic Safety Administration estimates 16,000 accidents per year in the United States occur when drivers intend to apply the brake but mistakenly apply the accelerator.
Definition and background In the 1980s, the U.S. National Highway Traffic Safety Administration (NHTSA) reported a narrow definition of sudden acceleration only from near standstill in their 1989 Sudden Acceleration Report:
"Sudden acceleration incidents" (SAI) are defined for the purpose of this report as unintended, unexpected, high-power accelerations from a stationary position or a very low initial speed accompanied by an apparent loss of braking effectiveness. In a typical scenario, the incident begins at the moment of shifting to "Drive" or "Reverse" from "Park". The report is taken from a study begun in 1986, in which the NHTSA examined ten vehicles suffering from an "above average" number of incident reports and concluded that those incidents must have resulted from driver error. In the lab tests, throttles were positioned to wide open prior to brake application in an attempt to replicate the circumstances of the incidents under study. However, the newest vehicle involved in the study was a 1986 model and no test vehicles were equipped with the electronic control (drive by wire) systems common in 2010. All vehicles were equipped with automatic transmissions, that is, no vehicles had manual transmissions with left foot clutch pedal disengagement of engine power. These tests were meant to simulate reports of the time suggesting that the vehicles were at a standstill and accelerated uncontrollably when shifted from park. With modern drive by wire fuel controls, problems are believed to occur exclusively while the vehicle is under way. General Motors cars of the 1950s with automatic transmissions have the R for reverse at the furthest clockwise position in the rotation of the column-mounted shift lever. L for low position is just adjacent as the lever moves one notch counterclockwise. Because it is very easy to select L, a forward position when desiring R, to reverse, there are many unintended lurches forward while the driver watches toward the rear, expecting to reverse the automobile. By the 1960s, gear selection arrangements became standardized in the familiar PRNDL, with reverse well away from the forward positions and between the Park and Neutral selections. The elimination of push-button drive control on all Chrysler products began after 1965 to eliminate the ease of selecting an unintended direction. The most prominent incidents of sudden unintended acceleration took place from 2000–2010 in Toyota and Lexus vehicles, resulting in up to 89 deaths and 52 injuries in the USA. The NHTSA first opened an auto defect investigation into Toyota vehicles in 2004, but the Office of Defects Investigation (ODI) within the NHTSA closed the investigation citing inconclusive evidence. Toyota also claimed that no defects existed and that the electronic control systems within the vehicles were unable to fail in a way that would result in an acceleration surge. More investigations were made but were unsuccessful in finding any defect until April 2008, when it was discovered that the driver-side trim on a 2004 Toyota Sienna could come loose and prevent the accelerator pedal from returning to its fully closed position. It was later discovered that the floor mats of the affected Toyota vehicles could cause them to accelerate suddenly and that Toyota had known about these problems but had misled consumers and continued to manufacture defective cars. In March 2014, the Department of Justice issued $1.2 billion of financial penalties against Toyota in a deferred prosecution agreement. In January 2021, engineer Colin O'Flynn was able to induce unintended acceleration with a similar Toyota vehicle using electromagnetic fault injection (EMFI) on a test bench. He used an ECU and components from a wrecked 2005 Toyota Corolla. O'Flynn's experiments were conducted without access to the ECU source code, and without access to the confidential report by the Barr Group. In late May 2022, Ford issued a recall for the 2021 Ford Mustang Mach-E due to an unintended acceleration issue resulting from the powertrain control module functional safety software potentially failing to detect a software error, resulting in unintended acceleration, unintended deceleration, or a loss of drive power.
Causes Sudden unintended acceleration incidents are often posited to involve the simultaneous failure of a vehicle's acceleration and brake systems. Acceleration system factors may include:
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