One of the basic safety margins in driving is the time headway drivers preserve with respect to cars ahead. Drivers have to detect decelerations of the lead car in order to this headway. Both perceptibility of the deceleration and expectations of the driver may influence the detection of a deceleration. This paper describes an experiment in a driving simulator in which the effects of these two factors on maintenance of time headway were investigated. Perceptibility of the deceleration did not affect maintenance of headway. Drivers react faster to decelerations that are easily perceptible, but they approach the lead car just as closely as when perceptibility is low. When drivers expect the lead car to decelerate, their response time is shorter. In addition, drivers increase their headway before the lead car has actually decelerated. This anticipatory behaviour allows drivers to preserve their preferred headway in a comfortable manner. (A)
Abstract