When it comes to traffic signs, red indicates that you’re supposed to stop. But it wasn’t always that way. Although traffic lights have always incorporated the red and green that we know today, stop signs used to be yellow.
The first stop sign was erected in Detroit, Michigan, in 1915. It was white with black lettering, which provided plenty of contrast for drivers. However, the original signs weren’t very eye-catching. Until the 1920s, other colors were used, and there was no standard color for a stop sign.
In the 1920s, however, yellow became the standard color for stop signs. Red was more desirable because it was already associated with stop. However, reflective technology did not exist, and red hues appeared dark at night. Moreover, red pigments faded in the sun.
Therefore, the standard color for a stop sign was yellow with black lettering. In 1954, the development of better pigments and coatings made it possible for red stop signs to maintain their vibrancy. The change from yellow to red also distinguished stop signs from yellow cautionary signs.
The octagonal shape of the stop sign was implemented much earlier than the red color, though. In the 1920s, engineers at the Mississippi Valley Association of State Highway Departments developed a caution-ranking system that relied on shapes. Circles were the most cautionary shape and were used for railway crossings. The octagonal stop sign fell immediately below the circle in regard to level of caution. One of the other reasons that an octagon was chosen as the shape of the stop sign is that it is easily recognized from the front or back.