Infrastructure-based technologies such as Signal Phase and Timing (SPaT) broadcasts have the potential to facilitate development and deployment of vehicle-to-infrastructure (V2I) applications using connected traffic signal infrastructure. To help evaluate use cases for SPaT broadcasts and connected traffic signal infrastructure, the Indiana Department of Transportation deployed Dedicated Short-Range Communication (DSRC) and cellular communication technologies at 11 intersections primarily along the U.S. Highway 231 corridor in West Lafayette. Researchers also developed several web dashboards, a web application, and a mobile app along with engaging with public and private sector stakeholders in field testing. The dashboards identified platoonable roadway sections using heat maps, locations with winter weather-related events, and probabilities of green lights depending on historic data and current travel behavior. The web application provided connected vehicle telemetry by distributing logged Basic Safety Messages (BSMs) with vehicle position, travel speeds, and other traffic information. The Maintenance Operations / Slow Moving Vehicle mobile app alerted drivers and motorists of slowdowns due to either road maintenance or slow vehicles. Researchers also developed a methodology for characterizing traffic signal phase change probabilities by the time of day.
- Obtain and use enhanced probe data to identify signal phase split failures, low roadway friction, and hard-braking events. Partnerships with the automotive industry could help facilitate data acquisition. These data could then be used to inform agencies of traffic signal timing needs, to identify road segments most impacted by winter weather, and to determine locations where drivers encounter conditions that result in hard braking.
- Enhance future connected vehicles by adding a “phase-next” window and reconsidering “free” timing. Signal controllers in the future could provide connected vehicles with a “phase-next” alert to update the vehicle’s phase predictions to improve accuracy. Similarly, because free timing used during overnight periods is based on random vehicle arrivals, traffic signal predictions for connected vehicles under free operations would be less accurate.
- Consider transmission latency and application requirements when determining the communication protocol for V2I implementation. The field experiments conducted in this study showed that the DSRC technologies had the lowest latency. Commercial cellular technologies for V2I tested in the study had a latency estimated at 630 ms, which was considered adequate for most use cases.