South Carolina Recommends Adaptive Signal Control Systems on Corridors With Traffic Volumes Between 20,000 and 50,000 Vehicles per Day and Speed Limits Between 40 and 55 mi/h.
Safety and Operational Impacts Were Evaluated Using A Crash Prediction Model in South Carolina.
Made Public Date
01/21/2022
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Identifier
2022-L01080

Adaptive Signal System Safety Impacts

Background

Adaptive Signal Control Systems (ASCS) are typically deployed to improve the operational performance of intersections and traffic corridors. ASCS change the signal timing of intersections in real-time to accommodate for changing traffic demand. The objective of this study was to evaluate the safety benefits of ASCS and determine the type of corridors best suited for ASCS implementation for traffic safety and operational improvements. A literature review and a nation-wide survey involved 28 states were conducted at the beginning of the research to identify ASCS corridor characteristics (e.g., design speed). The research team then evaluated the safety effectiveness of ASCS in terms of reducing the crash frequency at 11 ASCS corridors with a total of 109 signalized intersections in South Carolina. The specific questions that were focused on this study were: (i) the effect of ASCS on the crash frequency and severity, (ii) the effect of ASCS on the likelihood of secondary crashes on freeway sections that have alternate corridors with ASCS, (iii) the effectiveness of ASCS in terms of the travel time and travel time reliability, (iv) the type of corridors best suited for ASCS implementation for traffic safety and operational improvement.

Lessons Learned

Adaptive Signal Control Systems (ASCS) are typically deployed to improve the operational performance of intersections and traffic corridors. ASCS change the signal timing of intersections in real-time to accommodate for changing traffic demand. The objective of this study was to evaluate the safety benefits of ASCS and determine the type of corridors best suited for ASCS implementation for traffic safety and operational improvements. A literature review and a nation-wide survey involved 28 states were conducted at the beginning of the research to identify ASCS corridor characteristics (e.g., design speed). The research team then evaluated the safety effectiveness of ASCS in terms of reducing the crash frequency at 11 ASCS corridors with a total of 109 signalized intersections in South Carolina. The specific questions that were focused on this study were: (i) the effect of ASCS on the crash frequency and severity, (ii) the effect of ASCS on the likelihood of secondary crashes on freeway sections that have alternate corridors with ASCS, (iii) the effectiveness of ASCS in terms of the travel time and travel time reliability, (iv) the type of corridors best suited for ASCS implementation for traffic safety and operational improvement.

  • Deploy ASCS on corridors with an AADT between 20,000 and 50,000 vehicles/day and a speed limit between 40 to 55 miles per hour (mi/h). The statistical results of the study suggested that intersections on corridors with ASCS with AADT between 20,000 vehicles/day and 50,000 vehicles/day at major roads achieve higher safety benefits compared to ones with AADT less than or equal to 20,000 vehicles/day. In addition, the results suggested that intersections with a speed limit between 40 and 55 mi/h at major roads achieved higher safety benefit in terms of reduction in total number of crashes compared to the ones with a speed limit between 30 and 35 mi/h. ASCS was found to be effective regardless of intersection geometry (i.e., four-legged or T-intersections) if the two conditions are met.
  • Consider the speed limit difference between the major and minor approaches when deploying ASCS. The results suggested that when speed limit difference between major and minor approaches at an intersection as equal to or greater than 10 mi/h, and the average signal distance on a corridor is less than the threshold of 0.49 miles, the ASCS was more likely associated with lower crash severity. Deployment was also recommended if the speed limit difference is less than 10 mi/h, but the average distance is less than 0.69 miles. 
  • Take into account corridor characteristics to achieve operational benefits with ASCS. Based on findings of the operational evaluation analyses, the study suggested deploying ASCS on corridors if 1) the average speed of vehicles on a corridor is equal to or lower than 35 mi/h, 2) the number of traffic signals on a corridor is more than 10, 3) there are multiple peak periods (AM, Noon, or PM) on the corridor, and 4) the traffic conditions are variable or fluctuate by the hour.
Goal Areas
System Engineering Elements