Analysis and evaluation of the capacity of exit ramps at two-level interchanges in Lithuania

Abstract

In case of high right-hand traffic flow, the selection of appropriate configuration of exit ramp determines the smooth functioning of two-level interchanges. In foreign countries, i.e. in Germany, the USA, the Netherlands, Sweden or the UK the type of such exit ramps is selected according to the following criteria: the ratio between vehicles travelling on the main road and the ones that are turning right, as well as level of service. The maximum traffic flow that the exit ramp can permeate is prefigured. Since Lithuanians do not apply this method of exit ramp design and there is a clear dependence between the vehicles traveling on the main road and the vehicles exiting the main road, traffic conditions in this country have been assessed and modern traffic simulation software has been used in order to design and represent models of various exit ramp types for Lithuania. First of all, the behaviour of drivers exiting the main road at the two-level interchange was observed, and, after that, the video material was used to calibrate “Wiedelmann 99” algorithmic parameters for Lithuanian traffic conditions. Subsequently, in order to determine the capacity of each exit ramp, graphic nets were designed for every systemically created model with a specific traffic flow (the maximum capacity of one-lane exit ramp is 2000 vph; if there are vehicle queues and the capacity reaches 2450 vph, the two-lane exit ramp stops functioning). The key variable and the constant traffic flow value, which was used in different models, is 50 vph. Finally, four models of exit ramp at two-level interchanges were represented and limits of these models were determined.