Interstate 40 in Arizona

Interstate 40 (I-40) is an east–west Interstate Highway that has a 359.11-mile (577.93 km) section in the US state of Arizona, connecting sections in California and New Mexico. The Interstate is also referred to as the Purple Heart Trail to honor those wounded in combat who have received the Purple Heart. It enters Arizona from the west at a crossing of the Colorado River southwest of Kingman. It travels eastward across the northern portion of the state, connecting the cities of Kingman, Ash Fork, Williams, Flagstaff, Winslow, and Holbrook. I-40 continues into New Mexico, heading to Albuquerque. The highway has major junctions with U.S. Route 93 (US 93; the main highway connecting Phoenix and Las Vegas, Nevada) in Kingman and again approximately 22 miles (35 km) to the east and I-17 (the freeway linking Phoenix to northern Arizona) in Flagstaff.

For the majority of its routing through Arizona, I-40 follows the historic alignment of US 66. The lone exception is a stretch between Kingman and Ash Fork where US 66 took a more northerly, less direct route that is now State Route 66 (SR 66). Construction of I-40 was ongoing in the 1960s and 1970s and reached completion in 1984. With the completion of I-40 in 1984, the entire routing of US 66 had been bypassed by Interstate Highways which led to its decertification a year later in 1985.

I-40 enters Arizona from California at a bridge that crosses the Colorado River at Topock in Mohave County. It heads east from Topock and begins to curve toward the north at Franconia, completing the curve at Yucca. The Interstate continues to head north until it reaches Kingman. In this city, I-40 has a junction with US 93 at exit 48. US 93 heads toward the northwest from this interchange to Hoover Dam and Las Vegas. US 93 south begins to run concurrently with I-40 east as they both swing eastward through Kingman. The two later separate at exit 71 as US 93 heads toward the south toward Phoenix while I-40 continues east toward Flagstaff. Along the way, I-40 passes through the town of Seligman, then, at Ash Fork, it meets SR 89, the former U.S. Route that heads south to Prescott. Next, it passes through Williams, where it has an interchange with SR 64 (exit 165), which heads north toward Grand Canyon National Park. I-40 continues to the east to Flagstaff, where it has a major junction with I-17 at exit 195. I-17 heads south from this interchange to Phoenix.

East of Flagstaff, I-40 heads toward the east-southeast direction as it goes through the town of Winslow. It continues toward this direction until it reaches Holbrook, where it curves toward the northeast. Along this stretch, it passes through Petrified Forest National Park and continues to the northeast, passing through Chambers, and enters the Navajo Nation. The highway still continues to the northeast to the New Mexico border southwest of Gallup, New Mexico, as it continues on toward Albuquerque.

With the exception of a stretch between Kingman and Flagstaff, I-40 directly replaced the famed US 66 across northern Arizona. Where possible, US 66 was upgraded to Interstate standards to become I-40 directly. Exceptions to this were through the central business districts of the cities and towns that US 66 passed through, and I-40 had to be built as a bypass outside the cities. On October 26, 1984, after the last section of I-40 was completed in Williams, US 66 was removed from the state highway system of Arizona. The portions through cities that did not overlap I-40 would become business loops of I-40.

The routing of a road near the current corridor of I-40 in Arizona was first surveyed and built between 1857 and 1859. Lt. Edward Beale and his soldiers built the road along the 35th parallel that would come to be known as the Beale Wagon Road from Fort Smith, Arkansas, to the Colorado River to serve as a military wagon road. The road was a popular route for immigrants during the 1860s and 1870s until the transcontinental railroad was built across northern Arizona in the 1880s. In the early 1900s, the road became part of the National Old Trails Road, a transcontinental route from Baltimore, Maryland, to California, and the National Park to Park Highway, an auto trail linking the national parks of the west.

In the 1920s, as a nationwide system of highways called the United States Numbered Highways was being developed, the route through was given the designation of US 60. This designation was controversial since designations that are multiples of 10 are assigned to transcontinental east–west routes and this route was a diagonal route from Chicago, Illinois, to Los Angeles, California. As a compromise to states east of Chicago that felt US 60 should go through their state, a different route was given the number 60, while the route from Chicago to Los Angeles was given the number 66.

By 1927, the routing of US 66 through Arizona had been laid out, but none of it had been paved yet. By 1935, nearly the entire route had been paved, with the lone exceptions being a short stretch northeast of Valentine and a stretch between Peach Springs and Seligman. By 1938, the entire route in Arizona had been paved. In 1953, US 66 was realigned between the California border and Kingman to an alignment to the southeast to avoid the mountain curves and grades of the original alignment. By 1961, several sections of the highway had been expanded to a four-lane divided highway in anticipation of the coming Interstate Highway. Four-lane sections included a section near Ash Fork, another section east of Winslow, and a section east of Holbrook near the Petrified Forest National Monument.