A simulation study examining the implementation of BRT upgrades in Salt Lake City found benefits to implementing GPS-based TSP strategies, with low drawbacks.
Salt Lake City, Utah, United States
Improving Efficiency and Reliability of Bus Rapid Transit
Summary Information
Bus Rapid Transit (BRT) systems, which typically run in exclusive lanes with specially designed rail-like features, are popular for their effectiveness in promoting urban mobility. They have high capacity and low operational cost, which may be augmented by certain operational strategies to improve travel times and headway adherence. The most effective of these strategies is Transit Signal Priority (TSP), which is enabled by GPS-based technology and which provides data that may be further used to improve a BRT system's reliability.
The researchers, sponsored by the United States Department of Transportation, sought to analyze the effectiveness of both TSP and off-board fare collection. Several varieties of both operational strategies were reviewed. For the analysis, the study performed a microscopic simulation to test the TSP scenarios and implemented a data-driven optimization method to understand the contributing factor of off-board fare collection systems. The researchers also performed a literature review to understand the state of the practice.
METHODOLOGY
VSSIM, a microscopic, time-step and behavior-based simulation platform, was used for network modeling. Eight different scenarios were investigated, each with different variations of BRT implementation, GPS or traditional TSP, and further sophisticated varieties of TSP systems. The study corridor examined was an urban principal arterial in Salt Lake County. Findings were analyzed from the perspectives of transit operation, other non-transit operations along the corridor, and non-transit operations along side streets.
To understand the impact of fare collection systems, the researchers performed a heuristic optimization search over a number of variables. Passengers could be considered to board with or without needing to make a smart card payment, representing fare collection systems that relied on on-board fare collection and station-based fare collection respectively.
RESULTS
The analysis found that GPS-based TSP strategies can provide transit delay reductions and travel time savings as effective as traditional TSP tools, but with greater flexibility and lower equipment costs.
In particular, the combination of GPS-based TSP strategies with BRT upgrades achieved a total reduction in peak hour transit delay of 13 percent, with total savings in peak hour transit time of up to 9 percent.
Furthermore, the average non-transit travel time along the studied corridor did not differ significantly after the addition of TSP strategies and BRT upgrades. Non-transit side-street traffic, however, increased by up to 3 percent. There was not a significant impact on the average number of stops on side streets, indicating the overall impact was minor.
Because GPS-based TSP was found to be broadly as effective as traditional TSP strategies, the primary advantage was in the reduced installation costs.
The study found that while GPS-based TSP strategies provided transit delay reductions and travel time savings, they did so to a lesser extent than the implementation of BRT upgrades. Thus, a combination of the two would make the greatest impact.
