Overview
Chatham Area Transit and GDOT launched a Transit Signal Priority (TSP) project in Savannah to improve bus reliability and on-time performance. Using connected vehicle technology, buses running behind schedule receive extended green lights at 72 intersections. This system saves lives by reducing pedestrian and vehicle conflict at congested stops, saves time through more reliable transit service, and saves money via reduced delays. All of these benefits are accomplished through scalable infrastructure which is inter-operable with emergency vehicles and other future applications. Though early in deployment, the project shows promise in improving mobility and efficiency region-wide.
In this case study you will learn:
- How Transit Signal Priority improved bus reliability by extending green lights for delayed buses.
- How Georgia DOT’s connected infrastructure is scalable and can support future safety and mobility applications.
- How early collaboration among agencies ensured efficient deployment and long-term value for both transit operations and the broader transportation network.
Background
In May of 2022, representatives from Chatham Area Transit contacted GDOT with interest in pursuing Transit Signal Priority along several routes in the City of Savannah, with a desire to improve reliability and on-time performance of buses on these routes. Three routes along Waters Ave and Abercorn Street were identified as the most desirable for this system. These routes cross 72 traffic signals as they traverse the city, with two extending from downtown to midtown and the third from downtown to the southside.
With emerging V2X technology in recent years, this project was an excellent candidate for taking lessons learned through previous smaller pilot projects elsewhere in the state and expanding to a wider deployment.
TSMO Planning, Strategies and Deployment
Deployment of this TSP system required communication and collaboration between several different agencies and vendor partners.
An existing contract between GDOT and Atkins Realis was utilized to install Connected Vehicle Roadside Units capable of communicating over the 5.9 GHz band at 64 signals throughout the city. Locations where radios could not be installed due to construction isseues were enabled for TSP via peer-to-peer communications with nearby signals. These radios, while installed initially for the purpose of TSP, can be used for a number of additional safety and operations-focused applications in the future.
After-market on-board units were procured by GDOT and leased to the CAT at no cost for use on their buses. Research partner Southwest Research Institute worked with CAT and their AVL vendor to program the OBUs to place a request call at a signal if the bus is more than 5 minutes behind schedule.
Finally, implementation of the timing portion of the system was made seamless through GDOT’s mature, statewide, signal operations program, SigOps. Through the SigOps Southeast contract, Jacobs Engineering coordinated with the City of Savannah traffic engineering team to add prioritor timing to each signal controller. This timing allows for an extended green or early return to green for a bus that is behind schedule and has placed a request call. Peer-to-peer logic was used for signals without RSUs installed.
Communications Planning and Execution
Communication and coordination throughout this project were key to successful implementation. With so many partners at the table, it was essential to lay out roles and responsibilities from the onset. After a kickoff meeting with all parties, official updates on RSU deployment and OBU acquisition were conducted via email. A sign of successful working relationships between vendors and agencies, communication was also achieved throughout the deployment process via phone calls and field meetings as needed.
After deployment was complete and priority requests began being generated, additional meetings were held between GDOT, Savannah, CAT, Jacobs, Atkins Realis, and SwRI to discuss next steps and data evaluation.
Outcome, Benefits and Learnings
With 8 of 27 buses currently outfitted with OBUs, the system is currently in the early stages of operations. Data is being collected and evaluated in this initial operations phase but with little penetration rate, effects on on-time-percentage are difficult to measure. Once the remaining OBUs are installed GDOT aims to report on the rate of request calls placed throughout the system, and on-time-percentage on each route. Additionally, GDOT will conduct before/after analysis on the routes to measure any potential impact on the system to other traffic throughout the system.
Expected Benefit: The radios installed on this project operate with an interoperable architecture which can be re-applied to other cities, counties, emergency operators who are impacted by the same signals. This will lead to additional benefits to the City and its traveling public in the future.