The question of which colour to use for highway center lines (dividing opposing traffic) in the United States was the subject of considerable debate and changing standards over a period of several decades. It was the single most controversial and most heavily debated issue resolved by the promulgation of the 1948 edition of the "Manual on Uniform Traffic Control Devices" (MUTCD), which mandated white as the standard colour of center lines nationwide. The only exceptions to this standard were for double center lines on multi-lane highways and for center lines in no-passing zones, where yellow was recommended but not mandatory. By November 1954, 47 of the 48 states had adopted white as their standard colour for highway centerlines, with Oregon being the last holdout to use yellow. In 1958, the U.S. Bureau of Public Roads adopted white as the standard colour for the new interstate highway system.