Interstate 40 (I-40) is an east–west Interstate Highway that has a 359.11-mile (577.93 km) section in the U.S. state of Arizona, connecting sections in California and New Mexico. The section throughout Arizona is also known as the Purple Heart Trail. 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) in Kingman, the main highway connecting Phoenix and Las Vegas, Nevada, and I-17 in Flagstaff, the Interstate linking Phoenix and Flagstaff.
For the majority of its routing through Arizona, I-40 follows the historic alignment of U.S. Route 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. 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 towards the north at Franconia and completes the curve to the north 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 towards the northwest from this junction to Hoover Dam and Las Vegas. US 93 south begins to run concurrently with I-40 as they both head east through Kingman. The two separate at exit 71 as US 93 heads towards the south towards Phoenix while I-40 heads east towards Flagstaff. I-40 continues towards the east, passing through the town of Seligman and then at Ash Fork, where it meets State Route 89, the main highway that heads south to Prescott. Next, it passes through Williams at exit 165 with SR 64, and heads north towards Grand Canyon National Park. I-40 continues to the east to Flagstaff, where it has a junction with I-17 at exit 195. I-17 heads south from the interchange with I-40 to Phoenix.
East of Flagstaff, I-40 heads towards the east-southeast direction as it goes through the town of Winslow. It continues towards this direction until it reaches Holbrook, where it curves towards 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 towards 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.