Implementation of Highway Capacity Manual–Based Volume-Delay Functions in Regional Traffic Assignment Process

Abstract

Recent model development efforts for the travel demand forecasting process have focused on increasing the consistency and reasonableness of the results. A major target of these efforts has been the traffic assignment process and, more specifically, improving the estimates of congested travel speeds resulting from traffic assignments. A number of studies and enhancements have centered on the volume-delay functions used for the assignment process. Many of these studies have used the workhorse volume-delay function, the BPR function, and have investigated modifications to the function coefficients. In its recent update of the Albuquerque Area Travel Models, the Middle Rio Grande Council of Governments successfully implemented a regional traffic assignment process based on capacity estimation techniques and volume-delay functions documented in the Highway Capacity Manual. The assignment procedures developed for the Albuquerque area resulted in volume-delay functions that produced accurate traffic volumes while producing accurate congested speeds on the network. The capacity estimation procedures increase the realism of the network representation and provide increased analysis flexibility. Commercially available travel demand modeling software has been used to implement the Highway Capacity Manual–based volume-delay functions.