Sub-problem 5c: Pre-timed vs. Traffic-Actuated Operation

One of the purported benefits of traffic-actuated control is a more efficient timing plan. Appendix B of HCM Chapter 16 provides a method for estimating the average green times as a function of the traffic volumes, geometric configuration, left turn treatments, and detector parameters. The methodology of this appendix is iterative and somewhat complex analytically. It cannot be applied productively without software designed for the purpose.

While all of the controller and detector parameters can influence the cycle length and green times for actuated control, the most important setting is the maximum green time for each phase. The HCM suggests that it is clearly essential that some maximum green times must be imposed to control the apportionment of time between the competing phases. 

A number of techniques for assigning maximum green times have appeared in the literature. Most techniques involve some adjustment to the optimal green times for pre-timed operation. Three different ways of using the pre-timed optimal green times to determine the actuated average green times will be examined in this sub-problem:

1. Direct use of the optimal green times as average green times, as discussed in the first example in this sub-problem.
2. Application of the HCM appendix with maximum green times set equal to the optimal green times.
3. Application of the HCM appendix with maximum green times set equal to 150 percent of the optimal green times.