TRAFFIC STUDIES AT T-JUNCTIONS. 4. THE EFFECT OF SPEED ON GAP ACCEPTANCE AND CONFLICT RATE

Abstract

Gap acceptance for a simple crossing manoeuvre at a t-junction is measured and analysed in terms of the speed of approaching vehicles. The median accepted gap D in feet is related to the approach speed V in ft/sec by D = 115+1.9V (with D in metres, V in m/sec., D = 35+1.9V). The median accepted gap consists of a constant time of 1.9 sec plus a constant distance of 115 ft (35 M). This result, with a similar result for merging turns, is tested in a conflict simulation model. It is found that the fast drivers on the major road are more at risk than the slow drivers, and that the overall level of risk increases with increasing dispersion of speed. The bias of the observed gap acceptance functions is briefly discussed, and it is noted that gap acceptance may not by itself be a sufficient indicator of risk.(a) /TRRL/