Estimation of Volume Delay Functions for Urban Environments Based on an Analytical Intersection Model

This paper describes a method for estimating parameters in volume delay functions. The volume delay function is a central part of static traffic assignment models and describes how the travel time on road link changes with traffic demand. The proposed estimation method is based on that the volume delay function is divided into two parts, one part describing the link travel time and delay and one part describing the intersection delay. The parameters for the link and intersection parts are estimated separately. Collecting data for the link part is seldom a problem. However, earlier experiences have shown that it is both difficult and expensive to collect data on intersection delay. We have used an approach in which the intersection delay data is taken from a model for calculating intersection delay, in this case the analytical intersection model CAPCAL. The developed estimation method has been exemplified on one road type and road environment. A sensitivity analysis has been conducted in order to investigate how large influence that the different assumptions on the road factors have on the volume delay function. The conclusions are that the flow levels on the cross road, the intersection density, the share of straight forward traffic, and the share of different intersection types has the largest influence, and thus should be prioritized when collecting road type data.