In what year did the US stop sign change from yellow to red? The answer is 1954.
Early American stop signs used a yellow background because durable, fade-resistant red materials were not yet widely available. From 1924 through 1954, the signs generally carried a red or black legend on yellow, although designs and specifications varied between jurisdictions.
The 1954 edition of the Manual on Uniform Traffic Control Devices specified white lettering on a red field. This change aligned stop signs with the established meaning of red in traffic signals: stop. The octagonal shape, standardized in the United States during the 1920s, remained unchanged.
A common mix-up is 1935, when the first national MUTCD was published, or 1948, when retroreflective stop signs were required. Neither date marks the color change. The 1954 standard introduced the familiar red-and-white appearance that later became common internationally, including through the 1968 Vienna Convention on Road Signs and Signals.