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Strategies for Signal Timing and Coordination for Bicycle Progression
Civil and Environmental Engineering
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Current signal timing practices in the United States typically give vehicles the highest priority which can make travel by other modes challenging or time consuming. Bicycles are an example of these other modes that are not often prioritized. Due to their generally slow speeds, cyclists typically cannot keep up with timing plans designed for vehicle speeds. This can lead to increased stops and delays, souring the cycling experience.In places that do accommodate cyclists like the Netherlands, standard practice is to coordinate signals by designing for bicycle speeds. In the US, cities like Portland, OR and San Francisco, CA have adopted this practice in places, lowering speed limits and coordinating for bikes, and have become known for their relatively high numbers of cyclists. The other approach to this problem is to keep vehicles at their own speeds, but to also consider bicycle progression. Due to its complexity, this approach is much less popular. At the time of this research, there are few papers or case studies taking this approach. This research looks into the second approach of coordinating with vehicles and bicycles traveling at different speeds. The effort of this research can be divided into a conceptual method and an empirical method. The first method uses the relationship between vehicle and bicycle speeds to determine optimal cycle lengths or split lengths to create bandwidth for both speeds. This conceptual method calculates precise timing parameters that can provide ideal results. However, the calculated parameters may not reasonably serve intersection demand and thus, this method is limited by whether road segment lengths and mode speeds produce useable values. The second method is a brute force approach that takes timing plans and empirically grades them on potential for vehicle and bicycle progression based on timing inputs and expected travel results. This grade is representative of the overall quality of a plan for both vehicle and bicycle progression and can quickly be compared with other plans. The grading was calibrated with simulation done using Vissim for the Center St corridor in Reno, Nevada. Previous signal timing practices typically coordinated for one mode and then adjusted where possible to improve progression for the other, making the second an afterthought in terms of the timing and performance. This research provides a method for designing signal timing while looking at both modes simultaneously for fairer treatment. Provided the calculated timing parameters are sufficient for demand, the first method gives values that can guarantee similar vehicle and bicycle progression, but the second method is more widely applicable and can be used if the requirements for the first method are not met. It is recommended to use the first method, the TTD-Cycle method, if applicable but the second, TSD Performance Estimator, serves as a generally applicable backup.