When was the First Traffic Light Invented?

The first recognizably modern electric traffic light was invented in 1912 by Lester Wire, a Utah law school dropout turned policeman. Wire’s two-color traffic light, placed at the intersection of 200 South and Main Street in Salt Lake City, looked like a birdhouse with lights placed in it.
But traffic control is an old, old idea. There are records that three men worked as traffic police at London Bridge in the 1720s to make sure that the traffic traveling across the River Thames rode on the left. Generally speaking, however, such measures were unusual. In past centuries, the fastest available transportation was the horse, and population densities were low. (Before 1900, over half of all Americans lived in rural areas!).
Faster transportation in the 19th century led to the development of lighted signals that could be seen from a moving vehicle at the then-unprecedented speed of 30 miles per hour. Electricity was uncommon at this point, so many railway signals used gas lamps to control train movements.
In 1868, in London, a modified version of one of these gas lamp signals was built to control traffic. Railway engineer John Peake Knight designed it. The signal was built outside Parliament to regulate traffic over the Westminster Bridge. The traffic signal was derived from a railway semaphore signal and was manually operated by the policeman who ordinarily controlled traffic. The experiment was initially a success, but after a few weeks Knight’s traffic light exploded, injuring the policeman who operated it. After the accident, the experiment was cancelled.
The idea was independently revived in the early 20th century by Lester Wire and a variety of other inventors. It seems that many people came up with the idea at the same time. For example, James Hoge designed another primitive traffic light in Cleveland in 1914, with a built-in buzzer to warn of light changes. As for Lester Wire, he continually made improvements to the traffic signal over the years. Unfortunately for Wire, he never patented the traffic signal, and never received a dime for his invention.