Red Light
Violation Detection

The 2 main violation detection methods are radar and buried road sensors. When a violation is detected a camera takes a photo of the violation. Many systems also record video.

Radar
A pole mounted radar aims a narrow beam that covers the vehicle detection zone. The beam is adjusted for the intersection violation line. The beam must be set to very tight tolerances. At least one red light camera manufacturer (Redflex) has used radar.

Radar Detection

Video Based
These systems are often used in conjunction with other sensors.

Buried Road Sensors
There are 3 types of buried road sensors.

• Inductive Loop
  An electrical loop roughly the size of a car. It detects a vehicle when it's magnetic field is disturbed by the metal in a vehicle.
• Peizo Ceramic Sensors
  These sensors detect road pressure change from a vehicle.
• Magneto Resistive Sensors
  These detectors use 2 sensors centered in each lane, and spaced 5 feet apart. Each sensor is about 4 inches in diameter (and 2 inches deep), is battery powered and uses a wireless connection (2.400 - 2.4835 GHz / 2 mW). American Traffic Solutions (ATS) is known to use these detectors.

Magneto Resistive Sensors

Magneto resistive sensors are also used to measure highway traffic speeds and vehicle length. The sensors are typically spaced 10 to 20 feet apart in this application.