Few people have had a larger or more positive impact on the way we drive than William Phelps Eno, sometimes called the “father of traffic safety.” The New York City-born Eno — who invented the stop sign around the dawn of the 20th century — once traced the inspiration for his career to a horse-drawn-carriage traffic jam he experienced as a child in Manhattan in 1867: “There were only about a dozen horses and carriages involved, and all that was needed was a little order to keep the traffic moving,” he later wrote. “Yet nobody knew exactly what to do; neither the drivers nor the police knew anything about the control of traffic.”
After his father’s death in 1898 left him with a multimillion-dollar inheritance, Eno devoted himself to creating a field that didn’t otherwise exist: traffic management. He developed the first traffic plans for New York, Paris, and London. In 1921, he founded the Washington, D.C.-based Eno Center for Transportation, a research foundation on multimodal transportation issues that still exists. One thing Eno didn’t do, however, is learn how to drive. Perhaps because he had such extensive knowledge of them, Eno distrusted automobiles and preferred riding horses. He died in Connecticut at the age of 86 in 1945 having never driven a car.
Though the first stop sign was a humble square, that design didn’t last long. In addition to being easily recognizable from both sides and easy to see at night, the octagon was chosen in the 1920s as part of a still-influential initiative in which the number of sides a sign has indicates the level of danger it's meant to warn against. Train crossing signs were circles (which can be thought of as having an infinite number of sides) because those crossings were considered the most hazardous, followed by octagonal stop signs for intersections and the like; diamond-shaped signs were also used for less perilous crossings, and rectangular ones were posted simply to convey information.