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Signal Timing Manual 2nd Edition

Source: Airton Kohls and NCHRP (Report 812)

The Transportation Research Board in cooperation with the US Department of Transportation Federal Highway Administration has just released the National Cooperative Highway Research Program (NCHRP) Report 812: Signal Timing Manual - Second Edition (STM2). It covers fundamentals and advanced concepts related to signal timing. The report addresses ways to develop a signal timing program based on the operating environment, users, user priorities by movement, and local operational objectives. In addition to covering basic and advanced signal timing concepts, this second edition of the Signal Timing Manual addresses establishment of a signal timing program including setting multimodal operational performance measures and outcomes, determining staffing needs, and monitoring and maintaining the system. Some of the advanced concepts addressed include the systems engineering process; adaptive signal control; preferential treatment (e.g., rail, transit, and emergency vehicles); and timing strategies for oversaturated conditions, special events, and inclement weather. The manual will be useful by traffic engineers and signal technicians at any agency operating traffic signals.

The Center for Transportation Research Traffic Signal Academy is already incorporating the updated material from he STM2 on its workshops. For additional information on the program and for registration, go to: http://trafficsignalacademy.utk.edu/

The STM2 has an increased focus on signal system users and their priorities. Current signal timing models tend to provide a one-size-fits-all approach to signal timing, which often leads to the incorrect assumption that the model provides the optimum solution. A traffic analyst simply inputs the data required by the model, hits the optimize button, and gives the optimized results to the appropriate person for implementation. The results largely reflect the model's priorities (generally some version of vehicle delay) for system users, which may or may not fit the needs of the actual operating environment or users (including pedestrians, bicycles, and transit).

The STM2 introduces an outcome based approach to signal timing, which allows the practitioner to develop signal timing based on the operating environment, users, user priorities by movement, and local operational objectives. Performance measures are then used to assess how well the objectives are being met. Once the objectives and performance measures are established, timing strategies and timing values can be chosen. The final steps of the process involve implementation and observation (i.e., determining if the timing strategies and values are working), as well as sustaining operations that meet the operational objectives through monitoring and maintenance.

Chapter 2 of the STM2 got my attention because it looks at elements of successful signal timing programs. Effective signal timing programs ensure that signal timing parameters are appropriate over the life of the traffic signal system, by monitoring all aspects of traffic signal implementation, operations, and maintenance consistent with community needs. A successful program requires agency staffing and maintenance funding that is consistent with the level of service planned.

Chapter 8 on implementation and maintenance is another very useful resource, especially for smaller agencies responsible for traffic signals' operation and maintenance. The last four chapters of the STM2 on advanced systems and applications present relevant information and rich detailed graphics that aids on the explanation of more complex topics.

For additional information on the Signal Timing Manual 2nd edition contact Dr. Airton Kohls (akohls@utk.edu) at the Center for Transportation Research.


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