Did you know that road signs are designed to signal the level of danger drivers need to be aware of by the number of sides they have? And stop signs, having eight sides, signal the second highest? (The round and thus effectively infinite-sided sign used to mark railroad crossings is the highest level.)

The first electric traffic light was installed in Cleveland, Ohio, in 1914. Like its predecessor from 1868, it used two colors—red and green. But by this time the railway industry had switched the meanings of green and white, so that green meant “go” and white meant “caution.” This was because the increasing use of gas and electric lighting meant t