In this part we leave the southern Wasatch Front, which we first entered in Part 6, and cross the Wasatch Range into southeastern Utah.

A substantial segment of this Part and most of the next are spent co-routed with US 191 (and of course historically US 50). U.S. Highway 191, much like US 395, has become a major through-route in its own right despite ostensibly being "merely" a spur. In fact, the modern US 191 includes virtually none of the highway as originally designed in 1926: originally US 191 ran from Idaho Falls to US 20 in Montana; today it doesn't even enter Idaho. At one time it even connected to its parent US 91 (Part 7) in Idaho Falls and Brigham City; now it enters neither, despite US 91's modern stub still existing in the latter.

The reason for US 191's total rerouting was, again, Interstate 15. By 1981, after I-15 was mostly built (which we traveled in Part 7 as well), US 191 was a small connector from West Yellowstone to Malta, MT. Utah and Wyoming got AASHTO to approve a new tourist route to link the National Parks, originally along an extension of US 163 north from Monument Valley, but instead along a new US 191 when Arizona signed on. This 1981 extension used mostly existing highways, with some new sections built to link them, including old US 187 in Wyoming plus several state routes and the northern segment of US 163 in Utah. This second incarnation connected to Interstate 40 in Sanders, AZ, and is what we will travel here and in Part 9.

US 191 was also the impetus for the decommissioning of the infamous US 666, the worst-numbered highway in American road history ("could it be ... Satan?"), originally quite logically designated as US 66's sixth spur sixth sheep's sick in 1926 from Gallup, NM to then-US 450 in Cortez. In 1942 it was extended west along US 66 and south to the Mexican border at US 80 in Douglas, AZ, then subsequently north in 1970 along an old routing of US 160 to what was then still US 163 in Monticello, UT. The route's unfortunate number and safety problems earned it the unofficial name of the "Devil's Highway" and a notorious reputation that grew over the decades. In 1992, Arizona complained that the signs were frequently stolen and asserted a numbering change was needed since US 66 hadn't existed since 1985; the Arizona segment was renumbered as an extension of US 191. The other states considered the change and came up with their own plans, encouraged by Navajo Nation leaders who believed the number and its safety record were hampering tourism. New Mexico proposed (the preposterous, since it's nowhere near US 93) US 393, which AASHTO countered with US 491 due to the US 191 connection in Monticello; no one objected and US 666 was officially decommissioned in the remaining states in 2003, by which point virtually all the remaining US 666 shields had been stolen by thieves and souvenir hunters. A nice picture of an old one in Arizona survives in the "American Psychos" segment in Natural Born Killers. Observed one sardonic Monticello resident in the Salt Lake Tribune, "We'll really miss all the potheads stopping and taking pictures of the Route 666 sign."

After the 1992 lengthening US 191 was also extended north in 1996 from Malta, MT to the Canadian border. Unlike its greatly diminished parent, US 191 remains a border-to-border route today, again broken up only by Yellowstone (like US 20). Today it stretches 1,624 miles.