who invented the 4 way automatic traffic light
William Potts (inventor) The first four-way traffic signal tower in the world was located at the Woodward and Michigan Avenue intersection in October 1920. The tower was manually operated and had 12 lamps, three in each direction. In December 1920, signals were added along Woodward Avenue at Grand River, State, Fort and Congress, but all were controlled from the manual tower at Woodward and Michigan.
Traffic-light signalling and operation In some parts of Canada, a flashing green (known as Advanced Green) light signals permission for a left turn before the opposing traffic is allowed to enter the intersection, i.e., oncoming traffic is facing a RED light. Similarly, a flashing green may be an Extended Green, for left turns after the opposing traffic's full green phase. The flashing light may be a "full" green, or a green left arrow, both meaning the same thing. At least one traffic light in Montreal (on the Island of Montreal, 'Right-on-Red' is not allowed), has a flashing right-turn arrow, indicating that the pedestrian crossing has a red light, so it is safe to turn right and drive across it. At some intersections in Winnipeg, Manitoba, a flashing green right-turn arrow appears with a red light when traffic from the right has a green flashing left-turn arrow and is not allowed to make a U-turn. In other parts of the same country (e.g., Vancouver) a flashing green light conveys a very different meaning: the crossing road has stop signs with no lights of its own, and oncoming traffic also has a flashing green, not a red stop-light. This functions the same as a European "priority" sign (a yellow-and-white diamond shaped sign indicating that the current street is a Priority or "main" road, which cross streets must yield to at uncontrolled junctions, opposite to the usual arrangement in many European countries), for which there is no direct equivalent in North America.