INTEGRATING LIGHT RAIL INTO A FREIGHT CORRIDOR AND ANALYZING TRAFFIC SIGNAL PREEMPTION WITH VISSIM

The findings of a traffic study conducted for the Dallas Area Rapid Transit are presented. The study investigated the traffic operation issues at railroad grade crossings in the city of Garland, Texas, where double-track light rail transit (LRT) will operate adjacent to an existing freight track operated by the Dallas-Garland Northeastern. The primary tool used in this study was VISSIM, a computer program with built-in capability and flexibility to model mixed traffic and transit operations at a microscopic level. The purpose of this study was to (a) identify the potential queuing problems at intersections in the vicinity of the grade crossings through traffic simulations, (b) evaluate the impact of the LRT operations on the local traffic network in terms of vehicular delay and level of service, and (c) recommend mitigation measures for the problem areas. The traffic operations of the local traffic network, with and without the LRT operations, were evaluated. Specifically, the intersection of Austin and Newman was studied with different types of traffic control and mitigation measures to identify the safest and the most efficient traffic control because of its proximity to one grade crossing in combination with the existing traffic conditions. Different study scenarios were established accordingly at the beginning of the study, and the results from the simulations were analyzed. The traffic analyses indicated that most study intersections may incur minor increases in peak-hour vehicular delay with the LRT in place due to the station-related traffic. However, the resultant levels of service were considered acceptable based on typical traffic engineering practice. Of the types of traffic control studied at the Newman/Austin intersection, a traffic signal with train preemption would provide efficient traffic control and the safest LRT operation at the grade crossing.