3.3 Traffic Signals – Unable to Detect Vehicles
Inductive loop detectors at traffic signal sites are used to trigger a phase and to optimise traffic signal control operations. Inductive loop detectors are placed in-ground near the stop line and they are subjected to stresses from vehicles. Loops can get damaged once the pavement protecting them cracks or erodes to expose the detector. Premature damage often occurs if the loops are not properly installed.
Inaccurate or broken detectors will either fail to register a phase call or provide inaccurate inputs to the traffic signal control algorithm causing sub-optimal operation. Traffic signal control protocols allow the signal controller to compensate when a detector fault is suspected and alternative phase settings are implemented.
The current practice of scheduled site investigation and on‑condition‑based maintenance was considered beneficial and needs to be continued. In general, detailed guidance cannot be given on the frequency and intensity of operational maintenance as it is dependent on the specific nature of the equipment, its environment and the level of service it is required to perform.
However, the approach to installation and commissioning of signals needs to be modified to ensure that premature failures are minimised. This also includes further training of technicians, particularly when dealing with termination points.
It was also recommended that fail-safe protocols be implemented in traffic signal controllers such that faulty or unavailable detector are compensated operationally. Further, the ability to interrogate historical detectors readings to quickly identify potential detector faults needs to be considered. Road agencies need to develop their own application of the RCM tools to suit their environment and situation.
An example of the RCM process applied to traffic signals where the signals do not detect vehicles is presented in Case Study 4.
|Most prominent failure mode|
|Determine criticality||Failure consequence|
|List possible task (if applicable)||On-condition maintenance task|
|Scheduled restoration/replacement task|
|Change operating procedure|
|Change in commissioning (installation to site)|