Interstate 40, a major east-west route of the Interstate Highway System, has its western terminus in Barstow, California, United States. Known as the Needles Freeway, it heads east from Barstow across the Mojave Desert in San Bernardino County to Needles, before it crosses into Arizona west of Kingman.
Interstate 40 is a principal route to the South Rim of the Grand Canyon, with the exits leading into Grand Canyon National Park in Williams and Flagstaff.
I-40 used to have a conventional mileage sign in New Mexico to the east of San Jon (a village to the east of Tucumcari, New Mexico) which probably bore the longest distance on such a sign. The sign showed 1007 miles for Los Angeles, although I-40 doesn't actually go there (it is accessed via Interstates 15 and 10).
Numerous roads throughout the state connect directly to the interstate in violation of Interstate Highway Standards.
In the west Texas panhandle area, there are several ranch roads connected directly to the interstate. One of the marked at-grade crossings is shown to the left.
Interstate 40 flows through the heart of the state, passing through many cities and towns of Oklahoma. Some of them include Erick, Sayre, Elk City, Clinton, Weatherford, El Reno, Oklahoma City, Shawnee, Okemah, Henryetta, Checotah, Sallisaw, and Roland.
I-40 passes through six major cities in Arkansas: Fort Smith and Russellville on the western side, Conway and North Little Rock in the center, and Brinkley and West Memphis on the eastern side. It is a major thoroughfare for commerce as it is currently the only west/east interstate in Arkansas. In addition to this traffic, I-30's eastbound termination and merger with I-40 in North Little Rock cause the east side of the state to be inundated with more commercial traffic than the west side.
More miles of Interstate 40 pass through Tennessee than any other state. The interstate itself goes through the three largest cities in Tennessee: Memphis, Nashville, and Knoxville. Dandridge, Jackson, Crossville, and Cookeville are other notable cities and/or towns that I-40 travels through. I-40 goes through all of the three Grand Divisions of Tennessee. Before leaving the state, I-40 emerges into the Great Smoky Mountains. In May 2008, the portion of I-40 in Knoxville will be under construction for around 14 months.
In North Carolina, I-40 merges with I-85 between Greensboro and Hillsborough, just west of Durham. In Alamance County, the highway is also known as the Sam Hunt Freeway. Due to a recent rerouting of I-85 around Greensboro, I-40 departs from it eight miles (13 km) east of the original split. However, I-40 will be moved to a new alignment south of Greensboro, which currently carries the new I-85 bypass and will eventually carry Interstate 73 as well. The existing I-40 through Greensboro will become a second I-40 freeway Business Loop once the new alignment is finished by 2007. The concurrency with I-85 will be extended another 12 miles (19 km) on this new alignment.
In violation of Interstate standards, I-40 has one marked and two unmarked at-grade crossings in western North Carolina. About eight miles (13 km) from the Tennessee border in North Carolina, when going westbound, a sign for "Hurricane Road" will appear. Hurricane Road is a local dirt road whose quality is below that of the breakdown lane, and the intersection is controlled by a stop sign. It is a right-in, right-out entrance. A couple other unmarked local roads also directly link onto I-40 in the area, including a private access road for Walters Dam between mile markers 11 and 12 on the westbound side.