2.8Operation#
2.8.1Monitoring portable traffic signal systems#
The performance of the PTSS shall be monitored to ensure that the assumptions made for the system set-up are correct.
When monitoring and evaluating the operation of a site:
- Are traffic flows actually as predicted?
- Is traffic avoiding the signalised site, and creating congestion elsewhere?
- Is the equipment (controller) operating as designed?
- Are signal phasings and timings adequate?
- Are yellow times appropriate (in relation to vehicle stopping characteristics, and times provided between phases to clear traffic from the controlled area)?
- Is traffic being held for long periods of time at a red signal, when adequate gaps exist in a running movement?
- Are there delays to vehicles (and pedestrians) on each approach?
- Is the number of vehicles left in a queue at the termination of the green period, and the number of vehicles stopped more than once in each queue, at satisfactory levels?
- Are vehicle detectors appropriately located to detect traffic as intended, in both the passage and presence mode?
- Are unusual vehicles being missed by detectors, and are they in sufficient numbers to justify special detection techniques?
The following checks shall be made to ensure the correct operation of PTSS:
- When operating in unattended operation, Type-2 PTSS shall be inspected to confirm its correct operation at least once every 24 hours or shall have remote error monitoring and reporting functionality. Contact details of the relevant persons shall be available on the body of PTSS for reporting any fault with the PTSS.
- With Type-1 and Type-2 PTSS, an alternative control arrangement shall be available to be put in place if the PTSS fails.
- For Type-1 PTSS, Traffic Controllers and STOP / SLOW bats should be available in case of failure of the PTSS.
2.8.2Trouble shooting vehicle actuated operation#
Table 2.8.2 – Trouble shooting in vehicle actuated operation (Type-2 PTSS)
| Problem | Cause | Remedy |
|---|---|---|
| Long queues | Green time too short | Increase maximum green time setting (do not exceed the value given in the Table 2.7.4(a)) |
| Long queues | Vehicle detector fault | Call service, and operate as fixed-time or manual operation until fixed |
| Long queues | Capacity exceeded | Call supervisor |
| Signals do not change | Vehicle detector fault | Call service, and operate as fixed-time or manual operation until fixed |
| Green period is always the same length and longer than required | Vehicle detector fault | Call service, operate as fixed-time or manual operation until fixed |
| Traffic still in work zone at start of opposite green | All-red time too short | Increase all-red time setting |
| Long gap between last vehicle clearing and start of next green | All-red time too long | Decrease all-red time setting |
| Long gap between last vehicle clearing and start of next green | Vehicle detector fault | Call service, and operate as fixed-time or manual operation until fixed |
| Signals do not dwell on all-red time in absence of traffic | Vehicle detector fault | Call service, and operate as fixed-time or manual operation until fixed |
2.8.3Adjusting green time for fixed-time operation#
If the green times of Type-2 PTSS are too short (that is, the queue does not clear in the first cycle), they should be increased gradually by:
- Switching the signals to manual mode for one or two cycles to clear the queue
- Switching back to fixed-time mode and count how many vehicles do not get through in the first cycle
- Adding two seconds of green time for each vehicle that does not clear the work site
- Observing the signals over three cycles and subtract green time if the queue clears before the end of the green time.
Vehicle-actuated operation shall be used if traffic volumes significantly change throughout the work shift (for example, if traffic volumes are considerably higher in the peak hour). If the signals are in fixed-time operation, the maximum green time shall be adjusted throughout the day to suit the prevailing traffic conditions.