Modeling the Traffic Impacts of Transit Facilities Using Dynamic Traffic Assignment


C. L. Melson, Boyles, S. D., and Machemehl, R. B., “Modeling the Traffic Impacts of Transit Facilities Using Dynamic Traffic Assignment,” TRB Annual Meeting. Transportation Research Board, Washington, D.C., 2013. Copy at


This paper demonstrates the capabilities and benefits of using dynamic traffic assignment (DTA) to
analyze traffic impacts caused by transit services. The City of Austin’s proposed urban rail system is used as a case study. The urban rail connects the CBD, the University of Texas at Austin campus, and other
large traffic generators. The majority of the rail system shares right-of-way with traffic. However, several
segments have completely dedicated guideway. Previous analyses have focused either on microsimulation
(which is limited in spatial area and does not consider route choice changes) or regional planning (which
typically lacks detailed inputs and does not directly model transit impedances in the traffic assignment
process). DTA provides a connection between these two methods: it can model route choice behavior
using realistic inputs at a fine time scale across a large spatial area. Five scenarios with varying mode split
percentages were modeled. At low ridership levels, corridors with major geometric modifications experienced more congestion. This caused travel pattern changes, increasing the volume on nearby
parallel corridors.