Can you flash your car lights and turn the traffic light green?

M-Alice:

Returning home from Lindbergh Field late at night, the taxi driver stopped for the traffic light at the corner of Laurel Street and India. He began to flash the taxi headlights on and off. The red light immediately turned green, and we went on our way. He said, "It works sometimes." Does this really work? Is it legal?

-- Robert Dilworth of Mission Hills

Key word here? "Sometimes." This cause-and-effect stuff is preeeetty tricky. The whole thing, really, is an urban legend that evolved when those small tubular things started showing up on top of traffic lights. They are sensors that detect a specific flashing-light pattern transmitted from fire engines and ambulances. Emergency vehicles can turn the traffic lights green as they approach intersections in order to stop cross traffic and speed their progress. As usual, the rest of us heard the story and remembered about, oh, ten percent of it and made up the rest to our own benefit. Your taxi driver is only one of many who believe that if you flash your headlights very fast, you can turn a traffic light green. But you can't. It works "sometimes" because some traffic lights will change from red to green when a car crosses over a sensor in the road, especially at night when traffic is light. Sorry. The System 1, Average Joe 0, as usual.