In 2024, public transit systems provided 7.6 billion passenger trips in the United States and approximately 1.6 billion trips in Canada, playing a vital role in many riders’ daily lives. Agencies receive constant pressure to improve reliability and on-time performance. After all, nobody wants to get stuck waiting for a bus or train that’s fifteen minutes late – or worse, never arrives at all.
Transit signal priority (TSP), which gives transit vehicles green lights when it would improve performance, can deliver meaningful improvements. But only if it works within the systems agencies already operate. However, while best-in-class TSP solutions are widely available, projects become more expensive and complex when existing signal infrastructure is not ready to support them.
That’s why it’s so important that transit signal priority solutions be interoperable with agencies’ existing infrastructure. Interoperability allows agencies to deploy signal priority in the right way for their fleet size, pre-existing infrastructure, and budget constraints.
The Reality of Transit Infrastructure
Transit signal priority projects don’t begin in a vacuum. Most agencies must manage complex pre-existing infrastructure, such as a mixture of old and new traffic signal controllers. While the transportation industry is moving towards standards like NTCIP 1211 for transit signal priority communications, many older controllers in the field do not support these newer standards. When existing signal infrastructure must be upgraded to implement TSP, this can add cost and complexity to the project.
Applied Information’s Glance transit signal priority is designed to work with this reality. Glance integrates with all traffic controller types used in North America, from decades-old equipment, like 980 and 170 controllers, to the newest models. This interoperability allows agencies to provide TSP consistently across transit systems, regardless of controller make, model, or software version, increasing access to TSP without requiring infrastructure upgrades.
Different Budgets and Fleet Sizes Have Different Needs
When considering how to implement transit signal priority, agencies must balance budget with the time it takes to install new equipment across a fleet.
Many fleets already operate with Automated Vehicle Location (AVL) technology. Glance can integrate with many commonly-used AVL providers, including Clever Devices, Swiftly, Vontas (Trapeze), Avail, and TripSpark, to gather the speed, heading, and location of each transit vehicle. However, many fleet AVLs operate with polling intervals of 15 to 30 seconds, while more effective transit signal priority systems require a polling frequency of 3 to 5 seconds or less.
Reducing AVL polling rates to near real-time can be expensive. In some cases, the cost of lowering polling frequency across a fleet exceeds the cost of installing dedicated onboard units that provide second-by-second communication. This creates a set of practical tradeoffs, based on agency priorities.
Three Common Paths to Transit Signal Priority
Interoperability allows agencies to choose the implementation approach that aligns with their operational goals and budget.
- AVL-only priority
Integrating Glance with existing AVL systems can be an effective entry point for agencies with large fleets, where reducing the polling rates may be more time- and cost-efficient than installing dedicated TSP units in all vehicles. Provided the existing AVL system supports near-real time polling, using its data for TSP avoids taking vehicles out of service, although agencies may experience reduced precision and less detailed reporting due to slower polling rates.
- Dedicated units installed on fleet vehicles
Installing a vehicle priority unit provides second-by-second GPS updates and improves reliability, using redundant cellular and radio communications to request priority. For agencies deploying priority on a smaller number of routes or vehicles, this approach can be more cost-effective than upgrading AVL polling rates across the entire fleet. However, this approach only enables unconditional priority.
- Hybrid: Vehicle priority unit + AVL
Some agencies choose to combine onboard units with AVL data. In these cases, the onboard unit provides real-time location and communications, while the AVL system supplies schedule adherence, occupancy rates, or headway information. This and AVL-only approaches support conditional priority strategies, such as requesting priority only when the bus is behind schedule, or to maintain a regular headway. Adding an onboard unit protects vehicles from loss of communications during a storm, AVL disruption, or other outage.
- Hybrid: Vehicle priority unit + GTFS (Static or Realtime)
Directly integrating the dedicated onboard unit with the fleet’s AVL can be a complex process, subject to strict IT requirements. If an agency is only interested in triggering priority when the bus is behind schedule, integration with the fleet’s GTFS Static or GTFS Realtime feeds can provide an effective alternative. Like other hybrid approaches, the onboard unit provides precise vehicle location information and reliable communications, while the GTFS feed provides schedule information. Integration with GTFS Realtime is a particularly viable alternative to direct AVL integration, as the additional schedule adherence information leads to improved performance over GTFS Static.
Unconditional priority may not align with agency goals. Always requesting early green lights can cause buses to run ahead of schedule and disrupt service reliability. Conditional priority can provide more efficient priority, but may rely on data from multiple sources, such as GTFS Realtime for schedule information, an onboard unit for the vehicle location, and an AVL system for passenger headcounts.
TSP’s effectiveness depends on reliable data sources and real time communications, but there are many ways to implement it that work with existing frameworks. With multiple options for data sources, Glance enables agencies to implement TSP in a way that fits their operational needs.
Designing for Real Transit Systems
Applied Information understands that transit agencies operate under real constraints. Budgets fluctuate. Infrastructure modernizes gradually. Different fleets have different needs. Glance is designed with those differing needs in mind.
Interoperability allows agencies to move forward without forcing tradeoffs they cannot afford. By integrating with controllers and data sources from multiple manufacturers, Glance helps agencies deploy transit signal priority in a way that is practical, scalable, and aligned with how transit systems actually operate.
Bus in Intersection
