A sensitivity analysis was performed on the transit signal priority (TSP) requesting threshold to evaluate its impact on bus performance and general traffic. Two distinct bus routes were evaluated to determine the optimal requesting threshold that would balance the positive impacts on bus performance with the negative impacts on general traffic. Route 217, a conventional bus route, and the Utah Valley Express (UVX), a bus rapid transit line, utilize a dedicated short-range communication (DSRC)-based TSP system as part of their normal, day-to-day operations. Using field-generated data exclusively, bus performance and general traffic were evaluated over a 7-month period from February through August 2019. Bus performance was evaluated through on-time performance (OTP), schedule deviation, travel time, and dwell time, while the traffic analysis was performed by evaluating split failure, change in green time, and the frequency at which TSP was served. The requesting thresholds evaluated for Route 217 were 5-, 3-, 2-, and 0-minutes, which stipulate how far behind schedule the bus must be in order to request TSP. For UVX, 5-minutes and 2-minutes, as well as ON and OFF scenarios were evaluated; ON meant the buses were always requesting regardless of how late they were, while OFF meant that no requests were made and operations would be as if there were no TSP at all. A combination of observational and statistical analyses concluded with convincing evidence that OTP, schedule deviation, and travel time improve as the requesting threshold approaches zero with negligible impacts to general traffic. For Route 217, as the requesting threshold changed from 3, to 2, to 0 minutes, OTP increased 2.0 and 2.5 percent, respectively, mean schedule deviation improved 15.9 and 20.9 seconds, respectively, and travel time decreased at 72 percent of timepoints. Meanwhile, negative impacts to traffic occurred if an increase in split failure was measured after TSP was served, a phenomenon observed a maximum of once every 43 minutes. For UVX, as the requesting threshold changed from 5, to 2 minutes, to ON, OTP increased 7.6 and 4.7 percent, respectively, mean schedule deviation improved 24.3 and 15.0 seconds, respectively, and travel time decreased between 72 percent of timepoints. Thus, it is concluded that under the TSP system as implemented, bus performance improves as the requesting threshold approaches zero with inconsequential impacts to general traffic.
College and Department
Ira A. Fulton College of Engineering and Technology
BYU ScholarsArchive Citation
Sheffield, Michael Harmon, "Impacts of Changing the Transit Signal Priority Requesting Threshold on Bus Performance and General Traffic: A Sensitivity Analysis" (2020). Theses and Dissertations. 8521.
transit signal priority, TSP, dedicated short-range communication, DSRC, lateness threshold, V2I, requesting threshold, OTP, schedule deviation, split failure, reliability