Traffic loops, also known as inductive loops, work by detecting changes in a magnetic field caused by a vehicle passing over them. They are essentially large coils of wire buried under the pavement.
Here's a breakdown of the process:
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Creating a Magnetic Field: An electrical current is sent through the loop of wire. This creates a magnetic field around the wire.
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Baseline State: The loop controller monitors the inductance of the loop, which represents the magnetic field's strength. This inductance remains constant in the absence of metal.
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Vehicle Detection: When a vehicle (containing metal) passes over the loop, the metal disrupts the magnetic field. This disruption changes the inductance of the loop.
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Signal Transmission: The loop detector senses this change in inductance. This change is a signal that tells the system a car is present.
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Traffic Light Control: The system then sends a signal to the traffic light controller, which uses this information to adjust the timing of the traffic lights. The logic varies, but it might extend the green light for the lane with the detected vehicle, shorten the green light for other lanes, or trigger a change in the light cycle to allow the detected vehicle to proceed.
In short, the system operates on the principle of electromagnetic induction. A constant electrical current flows through the wire loop, creating a magnetic field. The presence of a metal object (a vehicle) alters this magnetic field, causing a change in inductance. This change is detected and used to signal the presence of a vehicle to the traffic light control system.
