Utah’s Connected Vehicle Smart Transit Signal Priority Project deploys one of the first DSRC systems in regular operation in the United States.
Salt Lake City, Utah, United States
Redwood Road Transit Signal Priority project
Summary Information
In late 2014, the Utah Department of Transportation’s (UDOT) partnered with the Utah Transit Authority (UTA) on the Utah Smart Transit Signal Priority project that uses Connected Vehicle (CV) technology to enable conditional priority of transit vehicles at traffic signals, with the objective to improve the reliability of bus service while optimizing the use of available green time.
The project developed a schedule-checking module that built upon the Multi-Modal Intelligent Traffic Signal Systems (MMITSS) software created at the University of Arizona. Through the deployment of Dedicated Short-Range Communication (DSRC) radios, the traffic signal controller and a small computer in the signal cabinet were able to communicate back and forth with similar radios and computers installed in UTA buses, so that if a bus got behind schedule, the signal would grant the bus available additional green time to help it get back on schedule.
The DSRC radios were installed at 30 signalized intersections along Redwood Road, from 400 South to 8020 South to broadcast both Signal Phase and Timing (SPaT) and intersection geometry (MAP) messages. The SPaT messages provided real-time information about signal operations, such as which legs of the intersection have red lights or green lights, and when those configurations would change. The MAP messages defined how many lanes were in the intersection, whether each lane was a through lane or a turn lane, what the lane widths were, etc. MAP messages were created based on high-resolution aerial imagery and confirmed with field surveying.
DSRC on-board units were also installed in several UTA buses, along with small Linux computers. These systems were connected to power and communication systems on buses so that a bus schedule and occupancy could be queried by the MMITSS system. The on-board radios broadcast information about the bus location and heading, known as the Basic Safety Message (BSM), and a Signal Request Message (SRM) when threshold criteria were met.
The corridor became operational in November 2017.
Findings
- Transit reliability for bus route #217 improved by 12 percent
- Late bus arrivals decreased by 40 percent.
