Intercepting a moving traffic gap while avoiding collision with lead and trail vehicles: gap-related and boundary-related influences on drivers' speed regulations during approach to an intersection.

Using a fixed-base driving simulator, 15 participants actively drove their vehicle across a rural road toward an intersection. Their task was to safely cross the intersection, passing through a gap in the train of incoming traffic. Spatiotemporal task constraints were manipulated by varying the initial conditions (offsets) with respect to the time of arrival of the traffic gap at the intersection. Orthogonally manipulating the motion characteristics of the lead and trail vehicles forming the traffic gap allowed evaluating the influences of the global (gap-related) and local (lead/trail-vehicle-related) aspects of the inter-vehicular interval. The results revealed that the different initial offsets gave rise to functional, continuous and gradual adjustments in approach speed, initiated early on during approach to the intersection. Drivers systematically accelerated during the final stages of approach, on average crossing the gap slightly ahead of the center of the traffic gap. A special-purpose ANOVA demonstrated an influence of (global) gap characteristics such as gap size and speed. Further analyses demonstrated that the motion characteristics of the lead vehicle exerted a stronger influence on approach behavior than the motion characteristics of the trail vehicle. The results are interpreted as signing the online regulation of approach speed, concurrently based on intercepting the (center of the) traffic gap and avoiding collision with the lead and trail vehicles.