Cameras at Traffic Signals

This is an FYI to the thousands of people who read my blog...

If you are driving through Auburn, AL and you see little cameras mounted on or near the traffic signals, those are not speed detection cameras. Those cameras are there to replace the "old style" loops that use to be inserted into the pavement for purposes of vehicle presence detection (to trip the signal when a vehicle is detected). The cameras simply detect the presence of a vehicle and actuate the signals accordingly. The cameras are setup to be pointed at specific locations so that it can tell when vehicles are cued up, as well as detection of approaching vehicles. In theory, it can see your vehicle coming so that it can change the signal at the most efficient time.

There is a good explanation of these cameras here. That link is for the St. Louis area, but the information is relative for Auburn.

Another "myth" that people seem confused about is that the old style detectors in the pavement are simply a wire that forms a loop and a magnetic field. When a vehicle is on top of the loop, it affects the magnetic field and sends a signal to the traffic controller. Many people think that the signals are tripped by weight; This is not the case.

You can usually see where the loop detectors have been installed because there is a thin groove cut into the pavement that forms a rectangular loop in the lane. Sometimes these are paved over when the intersection is resurfaced, but they are usually reinstalled after resurfacing. Also, the sensitivity can be adjusted on the loop systems. Sometimes it is too sensitive and vehicles turning left from the other street will pass by and trip it.

In summary: Old intersections use wire loop detection in the pavement. New intersections use camera detection. Not all intersection have detection.