Loopdetektorer

Loopdetektorer, commonly called loop detectors, are sensors embedded in roadways to detect vehicles and provide data for traffic control systems. They are among the most widely used traffic-detector technologies due to their reliability, simplicity, and low cost.

Principle and construction: Most loop detectors are inductive loops formed by copper wire arranged in a circular or rectangular pattern and buried in the pavement. The loop acts as an inductor; when a vehicle is over the loop, the metal mass changes the inductance, producing a change in current that the detection unit recognizes. A controller converts these changes into a signal of vehicle presence or into more detailed data when multiple loops are used.

Installation and configurations: Loops are typically installed per lane and connected to an interface unit at the roadside or in a cabinet. In common configurations, two loops in sequence provide vehicle presence and speed estimates, enabling actuated signal control. In some systems, additional loops classify vehicles by length or estimate queue length.

Applications and limitations: Loop detectors feed traffic signals to optimize flow, support incident detection, and help manage ramps and arterials. They are robust and cost-effective but require road excavation for installation and periodic maintenance. They can be affected by moisture, pavement aging, or nearby metallic structures, and newer detector technologies may offer better classification or reduced installation impact.

Related technologies include inductive loop sensors and other traffic-detection systems.