Sub-problem 3a: Actuated Signal Detection and Signal Timing

How do signal timing parameters affect the phase length? As we have seen from the previous page, the green time for individual phases with actuated control is variable. The time assigned to each phase is governed by three parameters, the minimum green setting, the maximum green setting, and the unit extension, also known as the passage gap.

The time allotted to each phase is dependent on the demand at the intersection and these signal timing parameters. In the case where demand is light, the remaining time from each phase is reallocated to the coordinated phase. Pedestrians also have an influence on phase lengths, but for simplicity, within this first sub-problem we will ignore pedestrian effects.

Two other factors may change the passage gap of a phase: TBR, or time before reduction, and TTR, time to reduce the passage gap as the phase extends past the initial value of unit extension time. These factors help to catch the platoon as it moves along a corridor. The TBR defines the amount of time the unit extension is held steady at its higher initial value. After the TBR, the unit extension is reduced, since at this point the queue that was waiting for the light is moving at a steady speed across the detectors. The unit extension value is reduced in a linear manner to the minimum gap time. The time that passes from the TBR to when the unit extension is at the minimum gap time is the TTR. Exhibit 5-X below demonstrates this concept, with an inital passage gap of 2.5 s, a minimum gap of 1.0s, a TBR of 12s, and a TBR of 15s.

On the next page, we will apply this information to our example.