GUIDANCE FOR USING RED LIGHT CAMERAS
Federal Highway AdministrationNational Highway Traffic Safety Administration
March 20, 2003
LIST OF TABLES
RED LIGHT CAMERA PROGRAM IMPLEMENTATION
Vehicle detectors are used to trigger the camera to record a vehicle running a red light. Different vehicle detection technologies are available for this purpose.
Most red light camera systems employ pairs of inductive loops installed near the intersection at a location suitable for showing that a violation has occurred. It is critical for the system design and operation that the inductive loops be installed in the appropriate locations, consistent with the agency's definition of a violation. Red light camera systems may also employ piezoelements, video-based equipment, or radar devices for vehicle detection and tracking, as an alternative to or in conjunction with inductive loop detectors.
The placement of the vehicle detectors is critical to the integrity of the red light camera system and the citations developed from the photographic data.
For red light camera systems that document violations with two photographs, the first photograph should be taken to show the motor vehicle, that will be running the red light, at a location immediately before it enters the intersection against a red traffic signal indication. The vehicle detection equipment should be configured to detect the presence of the vehicle at the desired location and to initiate the first photograph being taken with the vehicle at that location. If the vehicle is detected after it has already entered the intersection, it cannot be determined with certainty from the photographs that the vehicle entered the intersection illegally and consequently, a citation should not be issued. The second photograph is taken after the vehicle has entered the intersection, at a time interval after the first photograph calculated to provide the best view of the vehicle and its license plate, where required, the driver's face.
For red light camera systems that document violations with video clips that show the vehicle running the red light continuously starting at a location before the vehicle enters the intersection against the red traffic signal indication, vehicle detection should be configured so that the video clip recording is initiated at an appropriate location.
The placement of inductive loop detectors immediately in advance of the intersection stop line for vehicle detection may require that existing stop line loop detectors used for the traffic signal operations need to be abandoned, re-located, or replaced with another type of vehicle detection system, such as video-based detection. Generally, a solution that accommodates vehicle detection requirements for both traffic signal operations and the red light camera system can be developed although there may be some additional costs for vehicle detection associated with the installation of the red light camera system equipment under these circumstances.