Arterial Signal Coordination with Uneven Double Cycling

Abstract

In arterial coordination, high traffic volume at large intersections often requires a long cycle length to achieve good two-way progression. This long cycle length, however, often causes excessive delay at some minor intersections where the traffic volume is low on cross streets. This research proposed mathematical optimization models to enable uneven double cycling (UDC) in arterial signal coordination to address this issue.

The study first developed a basic UDC model to maximize two-way bandwidths and minimize average delay of cross streets at UDC intersection. The concept of nominal red was introduced to describe bandwidth geometry at UDC intersections. Disjunctive programming technique was used to convert a mixed integer nonlinear programming problem into a mixed integer quadratic programming problem for computation efficiency. The study further improved the basic UDC model to consider pedestrian needs and enhanced the modeling through multicriterion optimization. The additional objectives included minimal arterial average delay and minimal arterial number stops at UDC intersections, maximal variable bandwidth, and maximal secondary bandwidth.

With all the mathematical models ready, numerical experiments in the study explored factors affecting the applicability of the UDC control scheme. Results of the numerical experiments provided thresholds of parameters for determining UDC applicability. A rule of thumb was that when the green time of an intersection in the peak direction is longer than that at the critical intersection by at least the sum of minimum green time and per phase lost time, UDC control might be beneficial at this intersection. The research then conducted a case study to evaluate the performance of various models on the field data of an arterial with four intersections. Comparing with conventional SC control under fixed timing, the UDC models significantly reduced delay at UDC intersections for both through and left turn movements, and reduced number stops at SC intersections. UDC control under actuated operation overcame the shortcoming of increasing arterial number of stops compared with fixed timing.

Finally, the advantages and disadvantages of UDC control were summarized, and preliminary guidelines were provided for UDC implementation. Future study topics were also recommended.