The aim of this study was to identify the perceptual and motor strategies used by car drivers to prospectively regulate the speed of approach to a preceding vehicle so as to avoid collision. In order to evaluate the possible effects of driving experience, two groups of participants were tested. The first group consisted of 13 participants with less than three years of driving experience (mean age 20.5 years) and the second group consisted of 13 participants with more than five years of driving experience (mean age 26.5 years). All participants were tested on a fixed-base simulator (INRETS SIM2) under 16 different experimental conditions, combining different initial speeds and different preceding vehicle speeds. In each condition, just before the driver reached a designated goal speed (60, 80, 100 or 120 km/h), another car, serving as a mask, overtook the controlled vehicle, placed itself at a 2 s distance ahead and adopted the participant's speed. After a variable time period, the mask vehicle changed lanes, revealing an obstacle vehicle (positioned at stopling distance from the mask) moving at a speed equal to 100, 67, 33 or 0% of the driver's car. Thus, situations ranged from no danger (preceding vehicle at the same speed) to imminent danger (stationary obstacle). Overall, less-experienced and experienced drivers showed similar behavioural patterns, that were both functional (allowing collision to be avoided) and adapted to the situation at hand, with more change intervening more rapidly for the more urgent situations. Varying systematically with the degree of emergency of the situation, drivers both changed gear and activated the footbrake once or several times. In critical situations, drivers initiated braking after a time period that depended on both inter-vehicle distance and relative speed. The analyses of the duration of braking activity revealed that braking itself seems to depend on a complex relation between inter-vehicle distance and relative speed. Braking intervened as a systematic function of the information carried in the pattern of optic expansion of the obstacle (i.e., tau and its rate of change over time tau-dot), indicating the role of dynamic visual information in the regulation of approach speed. In order to avoid upcoming collision, drivers seemed to use informational patterns contained in the optic flow emerging from the evolving inter-vehicle distance and relative speed to regulate the velocity of their vehicle. The means used to decelerate (engine braking and/or foot braking) was linked to the degree of emergency perceived. (Author/publisher)
Abstract