When did the first traffic light appear?

Everybody seems to think it's obvious traffic lights must have appeared after cars, but not so fast. In another "Tech before it's time" instance, it turns out the first working traffic light actually hit the road, so to speak, in 1868 outside the Houses of Parliament in London. It was gas lit, and operated manually by a policeman standing next to it. The trick is to realise there were many horses and carts on the roads then, which had exactly the same needs as motorised vehicles when it came to keeping what had become busy traffic moving.

The first traffic management system, to get technical, was in the form of three policemen standing by the road waving the carriages through. This was in 1722, again in London but this time on London Bridge.

Red means stop

Right from the start, the light for "stop" was red. There's a detailed history of the traffic light on Wikipedia.

Here's an example of an early version:

The first traffic light actually blew up

To the amusement of motorists everywhere since, the first traffic light actually exploded as a result of a gas leak and injured the police officer controlling it.