State Study Assessed Impacts of Transit Signal Priority on a Connected Vehicles Corridor.
Salt Lake City, Utah, United States
Transit Signal Progression Algorithm for Supporting Redwood Road Transit Signal Priority (TSP)
Summary Information
The Connected Vehicle (CV) corridor, built along an 11-mile long road with 30 signalized intersections in Salt Lake County, Utah in 2017, utilizing Dedicated Short-Range Communication (DSRC) technology, had the main goal of implementing Transit Signal Priority (TSP) when a bus runs behind its published schedule. Given this, the goal of this project was to compare the TSP performance within the aforementioned CV corridor before and after the signal retiming, which took place in October 2018 to provide better signal coordination for buses. This project developed a new TSP control logic based on CV technology that enables real-time communication between traffic signals and buses, providing access to real-time signal status and bus travel information. Field data from three different sources, DSRC, Utah Transit Authority (UTA), and Utah DOT (UDOT) Automated Traffic Signal Performance Measures (ATSPM), collected during August and September 2018 represented the ‘before’ period, and the field data from November and December 2018 represented the ‘after’ period for this study.
METHODOLOGY
For this CV-based TSP application, DSRC radios from four vendors were installed at 30 intersections and on several buses for communication between vehicles and roadside infrastructure. Small computers were also installed at each intersection to collect data. Transit vehicle performance data, including Basic Safety Message (BSM), Signal Request Message (SRM), Geofence (MAP), Signal Status Message (SSM), signal controller data from ATSPM, the reliability and occupancy datasets, passed through DSRC, was logged by the signal controller and merged with UTA's data. The reliability dataset included a timestamp, bus ID, arrival times, and bus status, while the occupancy dataset included passenger information and dwell times. The application software supporting the TSP application in this project was a revised version of Multi-Modal Intelligent Traffic Signal System (MMITSS), which was initially developed for the CV Pooled Fund Study.
FINDINGS
- On average, the TSP request approval rate was 33.13 percent before signal retiming, which increased to 35.29 percent after signal retiming.
- Average reliabilities for northbound (NB) and southbound (SB) directions with the CV corridor before signal retiming were 89.44 percent and 92.07 percent, respectively. After signal retiming, they improved to 92.09 percent and 93.28 percent, translating into 2.65 and 1.21 percent points’ improvement, respectively.
- Bus travel times before signal retiming were 4,107 seconds and 4,191 seconds, respectively along the NB and SB directions, which were observed as 3625.06 seconds and 4095.07 seconds after signal retiming. This equals a 11.7 percent reduction in NB travel times and a 2.3 percent reduction in SB travel times for the buses, possibly due to reduced running time, higher TSP request approval rate, and less stop time as TSP activation occurred more during the red interval.
