March 18, 2019 – South Portland, Maine recently installed the EMTRAC system to provide Transit Signal Priority (TSP) for their South Portland Bus Service. As a part of the TSP implementation project, city personnel worked with their consulting traffic-engineering firm, Sebago Technics, Inc., to conduct a study to determine the general benefits of TSP in South Portland and to compare RF/GPS-based TSP with optical-based TSP to determine if one technology outperformed the other.
While there are many studies regarding the benefits of TSP in larger metropolitan areas with dense networks of routes, there is very little published data on the use of TSP in less-dense systems similar to South Portland. The South Portland bus service currently has three long routes, which serve major destinations across the city and provide linkage to Portland and Scarborough.
As described in the study, “A bus can cross a signalized intersection in South Portland as many as 44 times on a round trip, and minimizing stops and/or reducing delays at these locations by implementing TSP was thought to be significant in terms of shortening scheduled travel times and increasing on-time reliability—two key performance measures of a successful transit operation.”
The South Portland study comprised three 28-day testing phases. The first 28-day testing phase recorded bus performance under existing conditions, with TSP programming on the traffic controllers disabled. The second phase represented bus timing with TSP enabled. The third phase recorded the differences between RF/GPS and optical-based activation for TSP. The optical system was a non-EMTRAC legacy brand.
Here are some of the key findings and recommendations as a result of the South Portland Bus project:
- The results of both field and calculated time savings was significant—representing a 44% reduction in the time spent at signalized intersections.
- The radio-based EMTRAC system outperformed the optical system due to the increase in TSP-activation distance. The average optical activation distance was 200 to 500 feet. The average EMTRAC activation distance was 1,500 to 2,000 feet.
In this study, the EMTRAC detection zones were limited in distance so they did not extend past preceding intersections. Typical transmission range for the EMTRAC system is well over 3,000 feet.
- In comparing the radio-based EMTRAC system with optical TSP, the EMTRAC system reduced intersection delays more than twice the amount of the optical-based system in almost every instance.
- Due to specific conditions (such as bus movement and coordination programming), the use of TSP is not advisable at every single intersection. As a result, project engineers recommended 1) relocating some equipment to intersections identified as more effectively reducing delay through the use of TSP, 2) purchasing additional equipment, and 3) optimizing the traffic system. The total budgetary cost of these actions was estimated at only $25,000.
Having completed this project, South Portland becomes the first city in Maine, New Hampshire, or Vermont where TSP is actively utilized.
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