the shapes to be used for road signs. These suggestions included the familiar circular railroad crossing sign and octagonal stop sign. In January 1927, the American Association of State Highway Officials (AASHO) published the Manual and Specifications for the Manufacture, Display, and Erection of U.S. Standard Road Markers and Signs to set standards for traffic control devices used on rural roads. Despite the title, this manual did not have any guidance on pavement markings. In the archaic American English of the 1920s, the term "road marker" was sometimes used to describe traffic control devices which modern speakers would now call "signs." In 1930, the National Conference on Street and Highway Safety (NCSHS) published the Manual on Street Traffic Signs, Signals, and Markings, which set similar standards for urban settings, but also added specific guidance on traffic signals, pavement markings, and safety zones. Although the two manuals were quite similar, both organizations immediately recognized that the existence of two slightly different manuals was unnecessarily awkward, and in 1931 AASHO and NCSHS formed a Joint Committee to develop a uniform standard for both urban streets and rural roads. This standard was the MUTCD. The original edition of the Manual on Uniform Traffic Control Devices for Streets and Highways was published in 1935. Since that time, subsequent editions of the manual have been published with numerous minor updates occurring between, each taking into consideration changes in usage and size of the nation's system of roads as well as improvements in technology. In 1942, the Joint Committee was expanded to include the Institute of Transportation Engineers, then known as the Institute of Traffic Engineers. The single most controversial and heavily debated issue during the early years of the MUTCD was the color of center lines on roads. The 1948 version of the MUTCD settled the debate in favor of white, and also changed the standard color of stop signs from yellow to red. However, the 1948 MUTCD also allowed for two major exceptions to white center lines: yellow was recommended but not mandatory for double center lines on multi-lane highways and for center lines in no-passing zones. In 1949, the United Nations Conference on Road and Motor Transport launched a research project to develop a worldwide uniform scheme for highway signs. In 1951, the UN conducted experiments in the U.S. to compare the effectiveness of national traffic sign standards from around the world. Signs