6.5.2 Phase Intervals
This section discusses the concepts of vehicle and pedestrian phase intervals.
Vehicle phase intervals
A phase consists of two major parts as shown in Figure 6.6, the ‘running’ part and the ‘clearance’ part. The running part of the phase is the portion between the start of the phase and the termination point. Once the termination point has been passed, the next phase has been determined and cannot be changed. The running part is divided into five sequential time periods or intervals:
- late start
- basic minimum green
- variable initial green
- extension green.
- Minimum green includes basic minimum and variable initial green (refer to Appendix G).
The clearance part of the phase is the portion of the phase between the termination point and the end of the phase. The clearance part is divided into three sequential time periods or intervals:
- early cut-off green
The early cut-off green period allows the termination of some signal groups earlier than others. For example, at paired intersections, the upstream signals may be terminated earlier than the downstream signals in order to minimise queuing on internal approaches. The yellow period is to provide sufficient warning of the termination of the phase and allow time for vehicles to proceed if unable to stop. The all-red time provides a safe clearance time for vehicles that cross the stop line late in the yellow period. It also allows filtering traffic to clear.
The intergreen is the period of time between the termination of a green display in one phase and the beginning of a green display in the next phase. This usually corresponds with the yellow and all‑red intervals.
Pedestrian phase intervals
Pedestrian movements are normally grouped with vehicle movements to form a phase and run concurrently with parallel vehicle movements when appropriate. If pedestrian movements are grouped into one phase without any vehicle movements, then it is said to be an exclusive pedestrian phase. Where turning vehicles can cross a pedestrian movement, it may be necessary to provide pedestrian protection.
The pedestrian movement is divided into three sequential time intervals:
- Walk 1
- Walk 2
- Clearance 1
- Clearance 2.
Figure 6.7 along with their relationship with parallel vehicle movement intervals where applicable.
Note: Where pedestrian countdown timers are used in lieu of a flashing don’t walk (Red) display, a yellow countdown timer replaces the flashing red signal and displays the number of seconds left for pedestrians to cross before the red don’t walk signal appears (see further discussion in a succeeding section).
The duration of the Walk display is divided into Walk 1 and Walk 2. Walk 1 is a timed interval to provide a minimum time for the display. This is intended to allow time for pedestrians to begin their crossing. Upon expiry of the Walk 1 interval, the pedestrian movement enters the untimed Walk 2 interval, where it rests until the display is terminated.
The Clearance 1 and Clearance 2 intervals provide time for the pedestrians to complete their crossing. When a pedestrian movement is introduced, the phase normally cannot terminate until the Clearance 1 interval has finished. (An exception is when the pedestrian movement is allowed to overlap.) The Clearance 2 interval can run concurrently with the phase clearance and should not be longer than the phase clearance period. The relationship between the end of the pedestrian movement and end of phase varies between jurisdictions. Some jurisdictions use a walking speed of 1.2 m/s in the calculation of clearance time and terminate the Clearance 2 interval at the end of Vehicle All Red; others adopt a walking speed of 1.5 m/s provided that the flashing don’t walk display does not overlap into the vehicle intergreen period. In practice, the timing outcomes are similar.
Because of the relatively long time that pedestrians take to cross a road, the pedestrian clearance can represent a significant amount of time which could have been used by vehicle movements in another phase. Therefore, pedestrian movements are usually introduced only by demand. An exception is in areas of high pedestrian demand, such as in the CBD during the day, where pedestrian phases may be introduced every cycle.
Pedestrians are normally grouped with vehicle movements to form a phase (Roads and Traffic Authority NSW 2008c). This grouping should be such that the pedestrian movement run concurrently with parallel vehicle movements when appropriate. Where turning vehicles can cross a pedestrian movement, it may be necessary to provide pedestrian protection. The degree of protection can vary but can general approaches include full protection for the duration of the pedestrian movement or protection only for the initial stages of the pedestrian movement. For further details on pedestrian protection see Commentary 13.
[see Commentary 13]
Pedestrian countdown timers
Pedestrian countdown timers (PCT) can be used to help to create a more pedestrian friendly environment by giving pedestrians more information and greater awareness of their ability to cross the road (Department of Planning, Transport and Infrastructure 2013). The timers enable pedestrians at the crossing to make better decisions when crossing the road. They better inform pedestrians about how many seconds they have left to safely cross the road before the red don't walk symbol is displayed. A yellow countdown timer replaces the flashing red signal and displays the number of seconds left for pedestrians to cross before the red don’t walk signal appears (Figure 6.7). The countdown covers Clearance 1 and Clearance 2 intervals.