Traffic signals use loop detection technology to ’see’ vehicles and bicyclists passing through an intersection. Loop detectors work by passing electrical currents through conductive cables inside the pavement. When a metallic object passes over the magnetic field generated by loop detectors, the disruption tells the traffic signal controller that someone is waiting at or passing through the intersection. Because bicycles are smaller than vehicles, it is often more difficult for bicyclists to be detected at a traffic signal. While more recent advances in detector technology have alleviated some of these concerns, it is important for cyclists to understand the best way to be ‘seen’ by the traffic signal.
Regular circular loops with no diagonal wiring require a bicyclist to roll over the left or the right sides of the loop. Highlighted in green in the image above, these locations provide the bicycle rim with the best rate of success for detection, because it maximizes the bicycle’s interaction with the loop’s magnetic field.
Bicyclists may notice that some loops are wired at an angle to traffic. As shown above, it is best to roll over the center of the loop when wired diagonally. This same rule of thumb applies whether or not the loop has several or just a single visible wire at an angle to traffic.
Some bicycle lanes feature extra-sensitive detector loops designed specifically for bicycles. Pictured above, these detection zone for these specialized bike loops is straight through the center of the two octagons.
Many new intersections feature camera-based video detection. In the photo shown, a camera is used to detect motorists and bicyclists at an intersection. The camera’s processor is able to detect bicyclists at the intersection approach. If no loop detectors are visible at the intersection, keep an eye out for cameras placed on the signal pole’s arm.
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