What shape is an American stop sign?
Stop sign an "Idaho stop" or "stop-as-yield". The Idaho law has been in effect since 1982 and has not been shown to be detrimental to safety. Cyclist advocacy groups have sought similar laws for other jurisdictions in the United States. Stop signs originated in Michigan in 1915. The first ones had black lettering on a white background and were , somewhat smaller than the current sign. As stop signs became more widespread, a committee supported by the American Association of State Highway Officials (AASHO) met in 1922 to standardize them and selected the octagonal shape that has been used in the United
Stop sign States ever since. The unique eight-sided shape of the sign allows drivers facing the back of the sign to identify that oncoming drivers have a stop sign and prevent confusion with other traffic signs. It was also chosen so that it could be identified easily at night since the original signs were not reflective. The National Conference on Street and Highway Safety (NCSHS), a group competing with AASHTO, advocated a smaller pink-on-yellow stop sign. These two organizations eventually merged to form the Joint Committee on Uniform Traffic Control Devices, which in 1935 published the first Manual on Uniform Traffic Control