Most of the City's traffic signals have a way to detect vehicles and bicycles. Some locations have a loop of wire placed in the roadway that can determine when a vehicle or bicycle is present. Many newer signals have the bicycle detector symbol (small bike symbol) on the loop in the locations where a cyclist is most likely to be detected by a signal.
In a few locations where traffic loops are not feasible, the City has used video detection. The video detection system works by providing an image to a small computer that can detect a change in the image and determine the presence of a vehicle or bicycle.
Video detection can sometimes be compromised by the environment: fog, dust, shadows, trees, headlights and the reflection of the son on the asphalt can all have adverse effects on the accuracy of detection.