US Highway 666 was the sixth and last branch route of Route 66. Unlike the other branches, it was not originally laid out in the Joint Board on Interstate Highways’ numbering plan of 1925. Its creation came a bit later, after a dispute regarding the number of the parent highway had been resolved.
Originally, the Joint Board had planned a transcontinental highway, to be called US Highway 60, running from Chicago to Los Angeles, with five branch routes. In January 1926 the American Association of State Highway Officials (AASHO, later AASHTO) agreed and approved the creation of US 60. By this time, a sixth branch had been added to the plan.
This sixth branch that would later become US 666 was commissioned as US 660 and ran from Gallup, New Mexico to Cortez, Colorado. At around the same time, AASHO approved another transcontinental highway from Virginia Beach, Virginia to Springfield, Missouri, and this route was to be designated either US 62 or US 66. When, a few months later, AASHO proposed to extend the route from Springfield on to Los Angeles, an immediate controversy arose.
Various states through which the highway would run, including Kentucky and Virginia, argued that the US 62 or 66 route through their states should carry a number ending in zero (US highway numbers ending in zero and one were important cross-country routes) since this route was to be extended across the country. The dispute was finally settled when the number 60 was reassigned to a highway running from Virginia Beach, Virginia to Los Angeles, and the Chicago-to-Los Angeles highway was assigned number 66.
This was the state of affairs until 1942, when the Coronado Trail in Arizona was incorporated into US 666, bringing its total length to just over 550 miles. A further addition came in June 1970, when some 50 miles were added to the route, extending it to Monticello, Utah. The highway itself was a tricky drive; long, winding stretches of narrow two-lane road up and down mountains, some as high as 9000 feet.
Another change to the routing of US 666 came in 1992. The decommissioning of Route 66 in 1985 caused the link between US 666 and its parent highway to be lost. This prompted the states of New Mexico and Arizona to petition AASHTO to renumber the segment between Gallup and Douglas, Arizona. The request was approved, and that segment became part of US Highway 191. The segment between Gallup and Monticello, Utah retained the 666 designation.
THE DEVIL’S HIGHWAY
Naturally, with such a number, it was not surprising that US 666 would eventually be the center of still more controversy. The number “666” is well known as the Biblical “number of the beast”, as found in Revelation 13:18: “Let him who has understanding calculate the number of the beast, for it is the number of a man: his number is 666.” The road soon became known as “The Devil’s Highway”, and all manner of mysterious events were ascribed to the highway. Amazingly, people along the route grew to believe that devilish forces were at work, causing more accidents than normal.
There had been calls over the years to change the number to something less 'satanic', but they went mostly unheeded until early in 2003. As part of his plan to renovate US 666, New Mexico governor Bill Richardson announced his support for changing the highway’s number. The highway departments of Utah and Colorado joined in the effort, and the states submitted the request to AASHTO. Ostensibly, the change was part of highway improvements to “provide an added degree of comfort for those using the road”. It soon became apparent, though, that the perceived diabolic connection was the real reason behind the change.
Initially, the states wanted to base the new number on US Highway 91, but as the numbers 191, 291, and 391 were already in use as state highways, they settled on US 393. However, this number implied that the route was a branch of US Highway 93, which ran nowhere near US 666. AASHTO instead suggested that the new number be a branch of US Highway 191, and be called US 491. The states agreed and, on May 31, 2003, US 666 ceased to exist as its signs came down and were replaced by US 491 signs.
Droz, Robert V., "Sequential List of US Highways", US Highways From US 1 to US 830. July 2003. <http://www.us-highways.com/us1830.htm> (March 2004)
Weingroff, Richard F., "U.S. 666: Beast of a Highway?", Federal Highway Administration Highway History. June 2003. <http://www.fhwa.dot.gov/infrastructure/us666.htm> (March 2004)