Phase Time Prediction for Traffic-Actuated Intersections

The Highway Capacity Manual (HCM) provides a methodology in Chapter 9 to estimate the capacity and level of service at a signalized intersection as a function of traffic characteristics and signal timing. At traffic-actuated intersections, the signal timing changes from cycle to cycle in response to traffic demand. An accurate prediction of average phase times and their corresponding cycle length is required to assess the performance of intersections controlled by traffic-actuated signals. The current technique suggested in Appendix II of HCM Chapter 9 for this purpose has not been well accepted. A more comprehensive methodology and a more satisfactory analytical model are described that predict traffic-actuated signal timing for both isolated and coordinated modes with actuated phases. The proposed methodology and model have been verified by simulation augmented by limited field studies. The results are encouraging with respect to their general reliability and their compatibility with the current HCM Chapter 9 structure.