Detectors are used to detect vehicles and activate actuated traffic signals. The detectors are typically the same length and location as the detector in the field. Presence detection zone lengths are typically coded as 30 – 90 ft from the stop bar or from the signal head in Vissim. Advance detection zones should be placed 400 to 600 ft from the stop bar and should not be more than 50 ft in length. The detector is assigned to the same signal controller as the signal with the same port number as the phase that it activates. For detectors that control pedestrian signals, it is best practice to overlap the detectors with the pedestrian signal heads to make sure that relatively small pedestrians activate the detector.