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Insight Denton: How do traffic lights detect cars and motorcycles, and why can’t they seem to detect bicyclists?

Many traffic lights won’t change from red to green unless an electronic system detects a vehicle approaching the intersection.

Several different systems are used to make the lights change.

Some of the oldest traffic lights in Denton, such as the Fort Worth Drive/Interstate 35E intersection, use loop detection. Buried under the pavement, a small electric current travels through a conductor creating a magnetic field. Every time someone drives over the loop, the change in the magnetic loop triggers the light’s traffic detection system. It doesn’t always work well for small vehicles, such as motorcycles and scooters.

About 10 years ago, engineers put video cameras at several major intersections, such as Congress Street and Carroll Boulevard, for traffic detection. At least four video cameras detect approaching traffic coming from each direction. The system works well, including detecting smaller vehicles. However, the cameras have trouble with shadows and detecting small vehicles behind larger ones. Their accuracy also drops during fog, heavy rain and other bad weather. Plus, crews have to clean the camera lenses frequently.

According to the city’s traffic engineer, Pritam Deshmukh, new traffic lights will be outfitted with the latest advancement, radar detection. Radar equipment mounted on a signal pole sends out high definition digital waves, detecting cars, trucks, motorcycles, bicycles and even pedestrians. The traffic detection system performs well in bad weather, too. The new lights at Carroll Boulevard and Crescent Street already have radar detection.

— Peggy Heinkel-Wolfe

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