Gap-acceptance data are used to determine intersection sight distance, capacity, queue length, and delay at unsignalised intersections. They have also been used to determine the need for a traffic signal, the capacity of a left-turn lane, and warrants for left-turn signal phasing and storage lanes. A field study was performed to determine the gap-acceptance values of truck and passenger car drivers at six intersections. Each intersection was formed by two 2-lane roads; the minor road was controlled by a stop sign. The data obtained in the field were evaluated by three methods: green shield, raff, and logit. The findings from the field studies were summarised into generalised values. Passenger car drivers had a 50% probability of accepting a gap of 6.5 Sec for both left and right turns and an 85% probability of accepting a gap of 8.25 sc at a moderate- to high-volume intersection. A 10.5-Sec gap represented the 85% probability of accepting a gap at an intersection where accepted gaps were influenced by low volume and the intersection's geometry. Truck drivers' 50% probability of accepting a gap was 8.5 Sec. At a high-volume location, 85% of the truck drivers accepted a 10-sec gap; at a low-volume location, 15.0 sec was the accepted gap value.
Abstract