The Value of an Accelerator Release Signal

Abstract

The value of a signal shown on the rear of an automobile when the accelerator is released was investigated by measuring (1) the magnitude of decelerations in coasting passenger cars, (2) the ability of drivers to detect coasting of a vehicle they are following, and (3) coasting periods used by a number of drivers on various trips. Coasting decelerations of a sample of passenger vehicles did not exceed 3 ft/sec ² . The driver's sensitivity (ΔH), the change in spacing necessary to detect coasting of a lead vehicle, was a direct function of the initial headway (H) with a median value ΔH = 0.12H. Instrumentation of a motor-pool automobile showed that most coasting durations were between 0.5 and 5 sec. with speed reductions of less than 4 mph. Release of the accelerator pedal was followed by braking on less than 50% of the coasting occasions. It was concluded that a coasting signal could not reliably indicate that braking would follow and was largely unnecessary for detection of coasting, but could aid in reducing the development of critical conditions when coasting periods exceed about 5 sec. A signal given only when coasting duration exceeds 5 sec. would not occur frequently and would provide valid information on most occasions.