Problem 4: Analysis

The traffic-actuated timing procedure requires three control parameters. 

1. Minimum phase times, considering driver expectancy and pedestrian requirements. The minimum times from the pretimed example (Sub-problem 1b) were used here.
2. Maximum phase times to assure a reasonable distribution of green time on cycles with heavy demand. The literature contains a variety of techniques for setting maximum green times. For purposes of this example, the maximum green times were set at 20% longer than the pretimed values.
3. Unit extension times to determine the length of the gap in arriving traffic at which a phase will terminate. Most traffic models, including the HCM, will yield lower delay estimates with lower unit extension times. As a practical constraint, however, the unit extension must be slightly longer than the maximum expected gap between vehicles departing from a queue, otherwise premature phase terminations will occur. For purposes of this example, the unit extension times were set to 3 seconds for single-lane operation and 2 seconds for multiple-lane operation.

[ Back ] [ Continue ] to Problem 5