This paper models the traffic at an unsignalised intersection with one-lane approaches to both major and minor roads. The arrivals on both roads are assumed to be semi-random. The distribution of gaps between vehicles in the major road is modelled by an ERLANG-3 distribution, which offers a more realistic fit to actual traffic conditions, although it makes the calculations more cumbersome. The model allows a single gap to be used by more than one vehicle, when the gapsize permits this, and it explicitly recognizes the effects of vehicles sharing a common lane in the minor road. Formulae for estimating the capacity of the minor road are derived analytically. This procedure can be applied to T-junctions and crossroads and also to a minor road with a right-turn bay. The estimation of the capacity at an unsignalised intersection, using the methods of the paper, requires extensive calculations because simplifying assumptions are minimised and a close description of the actual traffic is emphasised. However, the total effort of using the model can be reduced substantially by using certain nomographs and by taking advantage of the relative shortness of its computer program. The application of this procedure, either as described, or with extensions accounting for multilane approaches and/ or platooned arrivals on the main road, is straightforward.
Abstract