Skip to content


A Failed Loop Detector May be Slowing Traffic in Your Community

A Failed Loop Detector May be Slowing Traffic in Your Community

Have you ever wondered why you have been stopped by a traffic signal when there are no other cars in sight? The intersection is clear, yet the signal forces you to wait.

This may occur for several reasons. Faulty pedestrian pushbuttons may be to blame. Or, it may be the traffic signal was built without vehicle detection and therefore operates in a pre-timed pattern where the controller will change the signals from red to green and back again after a predetermined time interval. However, the most common cause is a faulty loop detector.

A loop detector is simply a coil of wire located a few inches beneath the road surface that acts as a metal detector when a small electrical current is applied. Loop detectors have been the workhorse of the signal industry for many years because of their relatively low initial installation cost.

The signal controller is programmed to provide a green light when a vehicle drives over the loop detector. Over time the wire can break or become damaged, causing the detector to fail. When this happens, the detector goes into fail-safe mode and continuously sends a message to the controller that a car is waiting at the red light. This makes the signal change when no cars are present and causes you to get stopped.

So, what are the options for correcting this unnecessary and frustrating situation?

In most cases, replacing the loop detectors is the simplest and most cost-effective short-term solution. More efficient solutions based on life-cycle costs can be radar detection, video detection and thermal imaging detection. Depending on your schedule and budget, you can select the solution that best fits your needs.

Josh Pennock, PE, PTOE, Senior Traffic Engineer

Josh Pennock, PE, PTOE 
Senior Traffic Engineer