A Methodology for Assessing Signal Timing Plans and Control Technology Under Varying Demands and Capacities

This paper describes a methodology for predicting the robustness of signal timing plans and their associated control technology under varying demand and capacity conditions.  The proposed methodology involves the selection of a signal timing analysis tool and the repeated application of that tool for various demand/saturation flow ratio scenarios that might occur at the critical bottleneck of the system during the selected peak period over the course of a year.  The results are then combined into estimates of whole year average performance and 95 percentile worst performance.   A new indicator of robustness, the probability of breakdown, is introduced for quickly comparing the robustness of alternative signal timing plans and signal controller technologies.  The methodology can be applied using either macroscopic or microscopic signal analysis tools.  The key is that the selected signal analysis tool be able to accurately emulate the signal control technology and timing plans in place in the signal system.   This paper illustrates the application of the proposed methodology on a 5 signal actuated-coordinated system on El Camino Real in San Mateo, California.  The whole year performance of the current timing plan is compared to a timing plan optimized for a much higher, 95% demand condition.  The results for this particular example show that while the 95% plan sacrifices performance at the low volume conditions, this is more than compensated by significantly improved performance for the higher volume conditions that can occur over the course of a year.