Traffic Light loop detectors .. this info may help you trigger stop lights that use the old fashion inductive loop detectors that are buried in the asphalt.
Video Camera stop light detectors:
"Over the past several years the Town has made a strong effort to install video detection when signals are replaced or significantly modified. The Town maintains 61 traffic signals and of those 43 signals are equipped with video detection. Unlike the traditional loop detectors which are cut into the road surface, the vide detectors are mounted above the intersection. Video detectors improves the overall function of the signal and are capable of detecting bicyclists." ( this info from the West Hartford Planning Dept.)