On this day in 1868, the very first traffic light was installed outside the Houses of Parliament in London! It was designed by a British railroad engineer and used the same signals that were used for train traffic. The first traffic light only had two settings – a horizontal bar that indicated “stop” and a bar lowered to a 45-degree angle that meant “caution”. Railroad companies used red to mean stop, partially because it’s the color with the longest wavelength, meaning it can be seen from farther distances. The first electric traffic light was developed by a Salt Lake City policeman in 1912. It only had red and green lights and was first installed in Cleveland. Traffic lights wouldn’t get a yellow light until 1920. Ashville, Ohio is home to the oldest working traffic light in the world. It was in use there from 1932 to 1982 and is now in a local museum. Learn more here.