We have the Mississippi Valley Association of State Highway Departments to thank for the stop sign’s iconic shape. In 1923, the association developed an influential set of recommendations about street-sign shapes whose impact is still felt today. The recommendations were based on a simple, albeit not exactly intuitive, idea: the more sides a sign has, the higher the danger level it invokes. By the engineers’ reckoning, the circle, which has an infinite number of sides, screamed danger and was recommended for railroad crossings. The octagon, with its eight sides, was used to denote the second-highest level. The diamond shape was for warning signs. And the rectangle and square shapes were used for informational signs. “You have to realize this was done by engineers, and engineers can be overly analytical,” says Gene Hawkins, a professor of civil engineering at Texas A&M University and the nation’s pre-eminent expert on the history of the stop sign.

BIG RED

It took a bit longer to determine the stop sign’s color. It wasn’t until 1935 that traffic engineers created the first uniform standards for the nation’s road signage, known as the Manual on Uniform Traffic Control Devices. It was 166 pages long and recommended a yellow stop sign with black letters. The 1954 revision, however, called for the stop sign to be red with white letters, in step with the color-coding system developed for the railroad and traffic signals. “Red has always been associated with stop,” Hawkins explains. “The problem was they could not produce a reflective material in red that would last. It just was not durable until companies came up with a product in the late ’40s, early ’50s.”

Today the stop sign is so ingrained in collective international driving culture that some experts are, counterintuitively, recommending doing away with it entirely. (Ejby, Denmark; Ipswich, England; and Ostend, Belgium, are already experimenting with a post-stop-sign world.) “The theory is that people will pay more attention to pedestrians and other vehicles and slow down in pedestrian areas if there are no signs, because they won’t know what to do,” Schank says. “That wouldn’t be possible if [Eno] hadn’t first introduced the stop sign.”