An attempt was made to analyze certain of the underlying factors that cause the lateral displacement of a vehicle away from a roadside object. The investigation was conducted in daylight and under free field conditions. For several conditions of object location and vehicle speed, the lateral position of the vehicle was measured continuously over a 5,000-ft specially prepared test track. The findings indicate that lateral displacement is a special case in the field of visual velocity perception. Relative to the observer, the displacing object effectively moves laterally across the retina with a definable angular velocity. Drivers react to this apparent velocity by determining when and how much they should displace on the basis of the time and distance at which that velocity increases sharply. Rationalization is offered for the effects of lateral displacement on highway capacity and as an important consideration in collision avoidance under low illumination levels and headlight glare.
Abstract