A Volume-Delay Function for Motorways Taking the Impact of Trucks on Traffic Flow into Consideration

Kurzfassung

Currently in transportation modeling, travel time is the most important factor in decisions regarding transport modes, destinations and routes. The calculation of travel time is deployed by volume-delay functions, a sub-model of route assignment procedure, using the correlation between increasing numbers of vehicles on a road and the road’s restrictive capacity. By investigating existing volume-delay functions, a clear gap is seen, demonstrating that current functions are not suited to reflect the empirically known large impact of trucks on passenger car travel times. This issue becomes crucial when transport models are used to reflect future scenarios where goods transportation is expected to be increased greatly, and when transport models cover passenger and commercial traffic together. This article presents a new volume-delay function which successfully covers trucks’ impact on traffic flow in the case of Germany very well, and with slightly deviations also North America. The function is developed by using ideal-type data for German motorways. The differences of American data (Highway Capacity Manual) and German data (Handbuch für die Bemessung von Straßenverkehrsanlagen) and their implications for volume-delay functions are also discussed.