Current route in Arizona: Defunct
Current route nationally: Defunct
Historical route in Arizona: Mexico line at Douglas
to NM line near Lupton
Existed: 1938 - 1992
Historical route nationally: Douglas, AZ to Gallup, NM to Monticello, UT
The Highway of the Beast. Along with 69, this is probably one of the less popular highway numbers, although I think it's pretty neat.
The road earned its nickname between Alpine and Clifton, going around hundreds of curves.
US 666 became an extension of US 191 in the 1992. ADOT says they did it for route continuity, and because a north-south route isn't supposed to have an even number, but you can guess why they really did it.
In 2003, New Mexico, Colorado, and Utah renumbered their remaining leg of US 666 to US 491. The FHWA has a history of the route.
When it was established, US 666 ended at US 80 just west of Douglas. In 1962, it was extended along US 80 to Pan American Blvd in Douglas, then along Pan American to the Mexican border. In 1971 it was cut back to its old end, and Pan American became BUSINESS US 666. Oddly, the Business route never touched its parent. When US 666 became 191, the Business route was renumbered to 191 as well.
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Last updated 6/7/2003