Gap acceptance parameters serve as important design parameters in determining capacity and delay performance at priority unsignalised intersections. This paper proposes a procedure of simultaneously estimating gap-acceptance parameters and capacity, based on aggregate flow data collected at priority unsignalised intersections. The capacity formula adopted here is an "almost" exact capacity formulation based on a fluid approximation concept. With the general Pearson Type III density function assumed for the mainstream headway, the capacity formula is expresses as a function of mainstream flow rates and parametrised by the critical gap, the follow-up time, and the shape parameter. In the estimation procedure, under certain assumptions the crossing vehicles are modelled as the binomial process, and one can proceed with parameter estimation using the maximum likelihood technique, given aggregate flow data collected in time intervals. Capacity estimates consistent with field observations can be obtained accordingly. (A)
Abstract