Maximizing Benefits of Signal Timing Optimization

In recent years, it seems that signal timing has become a tool-dependent and a less knowledge-based exercise. Based on the authors’ experience, many users expect signal timing tools to produce readily used results and some use it as such. It is quite frequent that many traffic engineers who develop signal timing plans don’t how controllers function, because they think it is someone else’s job! This approach has many flaws in it, primarily because many practitioners who develop signal timing plans don’t have the knowledge in signal controllers and may not know how to interpret the model’s output and translate them into signal timing parameters in a signal controller. Relying entirely on models will not help users understand how signal controller-based improvements can be performed by utilizing functions inherent in controllers. Equally important is the knowledge and judgment that should be exercised when selecting cycle lengths, splits and offsets; these shouldn’t be based entirely on what the models predict. One would expect that the concerns above would be discussed in a Signal Timing Manual, but apparently that hasn’t been the case yet. However, this knowledge can be obtained from peer-to-peer discussions, publications, and Signal Timing Forums. In fact, some universities (University of Idaho and Purdue University, for example) offer laboratory hands-on signal controller programming workshops, and ITE is also spearheading similar Webinars to spread this knowledge to young traffic engineers and signal timing technicians. This paper draws heavily on the experience used in a signal timing optimization project in Baltimore, Maryland consisting of 410 intersections and including a 275-signal CBD network, and others in Maryland and Virginia. Although the Synchro model was used extensively, significant improvements beyond the model’s results were realized by using sound judgment in selecting number of timing plans; cycle lengths, splits and offsets; network partitioning; and in-depth knowledge of signal controller functions such as offset transitioning options; force-off options; dynamic split selection; left-turn conditional service; zero offset options; Transit Signal Priority (TSP), etc. This paper outlines and discusses practices that have proved to be significant in maximizing the benefits of signal timing optimization.