Sudden Unintended Acceleration (SUA) is the unintended, unexpected, uncontrolled acceleration of a vehicle from a stationary position, low initial speed or at cruising speed, often accompanied by an apparent loss of braking effectiveness.[1] It is unclear whether problems are caused by driver error (e.g., pedal misapplication), mechanical or electrical problems with automobiles, or some combination of these factors.[2]
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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".[1]
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, it is important to note that the newest vehicle involved in the study was a 1986 model and that no test vehicles were equipped with manual transmissions or the electronic control (drive by wire) systems common in 2010.
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.
In the 1950s, General Motors automobiles with automatic transmissions placed the R for reverse at the furthest clockwise position in the rotation of the column-mounted shift lever. L for low position was just adjacent as one would move the lever one notch counterclockwise. Because it was very easy to select L, a forward position when desiring R, to reverse, there were many unintended lurches forward while the driver was watching 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.
Sudden unintended acceleration incidents often involve the simultaneous failure of a vehicle's acceleration and brake systems. Acceleration system factors may include:
Unintended acceleration resulting from pedal misapplication is a driver error wherein the driver presses the accelerator when braking is intended. Some shorter drivers' feet may not be long enough to touch the floor and pedals, making them more likely to press the wrong pedal due to a lack of proper spatial or tactile reference. Pedal misapplication may be related to pedal design and placement, as in cases where the brake and accelerator are too close to one another, or the accelerator pedal too large.
An unresponsive accelerator pedal may result from incursion: i.e., blockage by a foreign object, or any other mechanical interference with the pedal's operation — and may involve the accelerator or brake pedal. Throttle butterfly valves may become sluggish in operation or may stick in the closed position. When the driver pushes harder on the right foot, the valve may "pop" open to a point greater than that wanted by the driver, thus creating too much power and a lurch forward. Special solvent sprays are offered by all manufacturers and aftermarket jobbers to solve this very common problem.
Other problems may be implicated in the case of older vehicles equipped with carburetors. Weak, disconnected, or mis-connected throttle return springs, worn shot-pump barrels, chafed cable housings, and cables which jump their tracks in the throttle-body crank can all cause similar acceleration problems.
For drive-by-wire automobiles, a brake-accelerator interlock switch, or "smart throttle" would eliminate or at least curtail any instance of unintended acceleration not a result of pedal misapplication by causing the brake to override the throttle.[9] An unintended acceleration event would require the failure of such a mechanism if it were present. Such a solution would not be applicable to older vehicles lacking a drive-by-wire throttle.
Analyses conducted in the mid to late 1990s on Jeep Cherokee and Grand Cherokee vehicles concluded that hundreds of reported sudden accelerations in these vehicles were likely caused by an undesired current leakage pathway that resulted in actuation of the cruise control servo. When this occurred, typically at shift engage (moving the shift lever from park to reverse), the engine throttle would move to the wide open position. While the brakes were operational, operator response was often not quick enough to prevent an accident. Most of these events occurred in close confines in which rapid operator response would be necessary to prevent striking a person, fixed object or another vehicle. Many of these events occurred at car washes, and the Jeep Grand Cherokee continues to experience sudden acceleration at car washes across the country. A statistical analysis of SAIs in 1991 through 1995 Jeeps revealed that the root cause of these incidents could not be human error, as had been historically posited by NHTSA and auto manufacturers.[10]
Reported incidents of sudden acceleration, include:
During model years 1982-1987, Audi issued a series of recalls of Audi 5000 models[19] associated with reported incidents of sudden unintended acceleration linked to six deaths and 700 accidents.[19] At the time, National Highway Traffic Safety Administration ( NHTSA) was investigating 50 car models from 20 manufacturers for sudden surges of power.[20]
60 Minutes aired a report titled "Out of Control" on November 23, 1986,[21] featuring interviews with six people who had sued Audi after reporting unintended acceleration, including footage of an Audi 5000 ostensibly displaying a surge of acceleration while the brake pedal was depressed.[22][23][24] Subsequent investigation revealed that 60 Minutes had not disclosed they had engineered the vehicle's behavior — fitting a canister of compressed air on the passenger-side floor, linked via a hose to a hole drilled into the transmission[21][22] — the arrangement executed by one of the experts who had testified on behalf of a plaintiff in a then pending lawsuit against Audi's parent company.[25]
Audi contended, prior to findings by outside investigators,[20] that the problems were caused by driver error, specifically pedal misapplication.[20] Subsequently, the National Highway Traffic Safety Administration (NHTSA) concluded that the majority of unintended acceleration cases, including all the ones that prompted the 60 Minutes report, were caused by driver error such as confusion of pedals.[26] CBS did not acknowledge the test results of involved government agencies, but did acknowledge the similar results of another study.[27]
With the series of recall campaigns, Audi made several modifications; the first adjusted the distance between the brake and accelerator pedal on automatic-transmission models.[19] Later repairs, of 250,000 cars dating back to 1978, added a device requiring the driver to press the brake pedal before shifting out of park.[19] As a byproduct of sudden unintended acceleration, vehicles now include gear stick patterns and brake interlock mechanisms to prevent inadvertent gear selection.
Audi’s U.S. sales, which had reached 74,061 in 1985, dropped to 12,283 in 1991 and remained level for three years.[19] — with resale values falling dramatically.[28] Audi subsequently offered increased warranty protection [28] and renamed the affected models — with the 5000 becoming the 100 and 200 in 1989.[20] The company only reached the same level of U.S. sales again by model year 2000.[19]
As of early 2010, a class-action lawsuit filed in 1987 by about 7,500 Audi Audi 5000-model owners remains unsettled and is currently contested in county court in Chicago after appeals at the Illinois state and U.S. federal levels.[19] The plaintiffs in this lawsuit charge that on account of the sudden acceleration controversy, Audis had lost resale value.[22]