Empirical analyses of the effect of opposing left-turning and leading left-turning vehicles on capacity of intersections with dynamic sight distance problem.

摘要

Sight distance problem is generally associated with horizontal alignment, vertical alignment and stationary objects which may impede the line of sight of the motorist. Dynamic sight distance problem, however, is associated with objects in motion such as vehicles at intersections interfering with unprotected left turn movements. The theoretical effect of dynamic sight distance problem on operational condition of vehicles at intersections has been examined before; with findings indicating that the problem increases both the critical gaps and follow-up time, and as a result reduces the potential capacity at intersections.;Although critical gap and follow-up time currently being used by HCM include dynamic sight distance conditions, the values were not estimated to reflect the contributing effect of dynamic sight distance problems at the intersection. Therefore it is not known to what extent dynamic sight distance problem affects the operational conditions at intersections.;This research investigated empirically the effect of dynamic sight distance problem on the operational condition of vehicles at intersections. Primarily, it investigated the effect of two conditions associated with dynamic sight distance problem. The conditions are (1) the presence of left-turning vehicles in the opposing lane and (2) non-compact vehicles leading smaller vehicles or vehicles of the same size leading in a left-turn queue.;The critical gaps and follow-up times directly attributed to dynamic sight distance problem and without dynamic distance problem were determined empirically. The results were used to determine the intersection capacity based on the Highway Capacity Manual's model for estimating potential capacity.;The results show that dynamic sight distance problem increases critical gap and follow-up time, and also reduces capacity at intersections with unprotected left-turn movements. The empirical investigation concurs with results obtained from previous analytical investigation which concluded that the presence of moving vehicles along opposing left-turn lane and leading non-compact vehicles in a left-turn queue, two of the conditions associated with dynamic sight distance problem, increase the critical gap and follow-up time, and hence reduce capacity.