The first traffic light was operated by a policeman in 1868 and it was the only way things worked for a while.

Modern traffic control systems are implemented with microcontrollers, networks and software.

But what are the first mechanisms that allowed to free the traffic police from the mundane task of directing the traffic?

Was there a sort of an electric or mechanical timer? If so, how did it work? How were the automatic traffic lights synchronized?

All solutions that predate digital electronics are welcome.


1 Answer 1


In 1910 Ernest Sirrine had patented an automated street-traffic system that used a motor and a set of gears and pulleys to rotate signs attached to an axis.

... The cam 13 is driven at a constant speed and at a rate to suit the estimated proper speed of street traffic, and is of such a nature as to operate the arms 11 at proper intervals, this operation of these arms being simultaneous as they are linked at 16. Each time the arms 11 are operated both arms 7 and 8 are rotated about their fixed horizontal axes, whereby one arm displays one signal and the other arm displays and opposite signal each time the arms are rotated.

From that description, I guess you could say the first automated traffic light system used a mechanical timer, not synchronized with other traffic lights, but displaying opposite signals on both sides.

figure 4 from E.Sirrine's patent, showing the mechanism described above

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