9/2/2025 McCall Macomber
Written by McCall Macomber
Improving the efficiency of transit services not only allows users to reach their destinations quickly and reliably, but also reduces overall traffic congestion and energy consumption.
Illinois Center for Transportation and Illinois Department of Transportation aim to increase transit efficiency in a joint project, “R27-259: State Department of Transportation Support for Operationalizing Transit Signal Priority.”
Chuck Abraham, IDOT’s Manager of Program Support (Planning), and Taqhi Mohammed, Pace Suburban Bus transportation engineer, led the project with civil engineering professors Abolfazl (Kouros) Mohammadian, Alireza Talebpour and Mohammad Miralinaghi.
The team examined use of transit signal priority systems nationwide to improve applications in the Chicago metropolitan area.
“Transit signal priority allows a bus with relevant technology to communicate with a traffic signal controller,” Abraham said. “The traffic signal controller can adjust the traffic light’s timing to extend an existing green light or shorten a red light to allow the bus to go through the intersection, among other things.”
Successful use of these systems improves bus service reliability, reduces delays and increases operational efficiency, making bus services more competitive with car travel.
To identify barriers to successful implementation, the researchers interviewed personnel from state transportation agencies as well as transit and planning organizations and reviewed nationwide best practices on transit signal priority systems.
They used thematic analysis, a qualitative method that recognizes and analyzes patterns, to identify key themes from the interviews. They applied topic modeling, a form of AI used to detect patterns or themes in text, to find the main barriers to transit signal priority use.
Their findings revealed several factors that deter agencies from adopting transit signal priority systems such as organizational, policy, funding and technological challenges.
“This study suggested that CDOT [Chicago Department of Transportation], the CTA [Chicago Transit Authority], IDOT, Pace, and the RTA [Regional Transportation Authority] should regularly hold meetings to coordinate signal implementation,” Abraham said.
“Their job is difficult, however, because of personnel shortages, outdated or old traffic signal hardware, equipment compatibility, a reliance on fragmented funding sources, and many regulations,” he added.
The research team developed recommendations for IDOT to improve those areas, such as streamlining permit and review processes, establishing an entity to oversee permitting and approvals, and investing in a centralized control system, among others.
“This project highlights needs that, if resolved, can help make bus travel much more efficient, effective and reliable in Northeastern Illinois, especially if transit signal priority is combined with other technologies such as off-vehicle ticketing, priority turn lanes, and dedicated bus lanes,” Abraham said.