They are so ubiquitous that although we see them every day and although their existence has saved lives, we give them little thought except ‘stop on red; go on green’, but the humble traffic light is 101 years old today. Google is honoring the occasion with a doodle depicting the first electronic traffic lights, which were installed in Cleveland, Ohio on August 5, 1914.
The simple red and green design was the idea of a Salt Lake City policeman called Lester Wire. There was no middle yellow light. Instead, when the lights were about to change, bells or buzzers would go off. There have been variations on the design over the years, with some countries opting for the horizontal rather than the vertical, but in every country red means stop and go means green, even though some have argued those colors should be reversed as green is actually more visible to the eye.