6.7.12 Signal Controller Timing Settings
There are two major aspects of traffic signal timing:
- The determination of maximum cycle times and green times for each phase (sometimes called green splits). Determination of these is part of the design process for traffic signals.
- The determination of controller time settings. These are the more detailed settings that:
- ensure the safe operation of traffic at the signals, including yellow, all-red and pedestrian clearance timings
- for traffic-actuated signals, determine the behaviour of the signals under varying traffic conditions when maximum cycle times and green splits are not required.
These are discussed in this section. Appendix E presents a worked example of signal design which includes guidance on determining maximum cycle times and green times.
Table 6.8 provides a summary of the various signal timing purposes and settings required for safety and to minimise delay. Discussion of the basis for each setting and how they can be determined within the range given here is quite detailed and is therefore presented in Appendix G. Table 6.8 also provides a directory to the relevant section of Appendix G for each setting.
Accurate records of the time settings at traffic signals are essential. Remember, they may be called in legal proceedings. It is also important for records of time settings used in the past to be retained. Appendix E includes an example of a signal timing record card, a copy of which is usually kept in the controller housing for reference by visiting field staff.
|Setting||Purpose||Typical range||Appendix G reference|
|Maximum cycle time||Limit the total cycle time to reduce delays and queue lengths where applicable||
80–100 seconds (simple two-phase)|
130–160 seconds (complex phasing)
|Late start||Allow the introduction of some signal groups to be delayed for a preset time||0–6 seconds||Table G 1 |
|Basic minimum green||Ensure that the green signal is displayed for a safe minimum time||4–10 seconds||Table G 1 |
(for advance detectors)
|Add a small amount of time to the Basic Minimum Green Setting to provide extra green time for vehicles stored between the detector and the stop line||0.5–2.0 seconds||Appendix G.4.2|
|Maximum variable initial green (for advance detectors)||Limit the initial green period determined by increments||Depends on the distance of advance detectors from stop line||Appendix G.4.2|
|Maximum extension green (or maximum green)||Control the maximum extension green time (after minimum green intervals) available to each phase or signal group||Choose for optimum traffic performance under different traffic conditions; avoid unduly long cycle times||Table G 1 |
|Gap||Set the maximum allowable time period between successive detector actuations before the movement terminates (‘gaps out’)||1.0–4.0 seconds||Table G 1 |
|Early cut-off green||Allow the termination of some signal groups earlier than others||0–10 seconds||Table G 1 |
|Yellow time||To provide sufficient warning of the termination of the phase||3–6 seconds||Table G 1 |
|All-red time||Provide a safe clearance for vehicles that cross the stop line towards the end of the yellow interval||1–3 seconds||Table G 1 |
|Presence||Set the period for which a detector must be occupied before a demand is recorded||0–5 seconds||Table G 1 |
|Headway (space)||Set the desirable space time between successive detector actuations for efficient traffic flow||0.3–1.5 seconds||Table G 1 |
|Waste||Set the value of the sum of the excess of the actual space time over the space time setting at which the phase is terminated||4–12 seconds||Table G 1 |
|Minimum red arrow time||To allow appropriate red arrow display time considering driver reaction/perception characteristics||2–5 seconds||Appendix G.4.7|
|Pedestrian walk time||Set the duration of the green Walk display||5–16 seconds||Table G 1 |
|Pedestrian clearance time|
Set the duration of the flashing don’t walk
|6–20 seconds||Table G 1 |
|Pedestrian delay||Provide a delay between the start of a phase and the start of the Walk display||0–10 seconds||Appendix G.5.4|