Interstate 40 replaced much of historic Route 66 as a major cross-country route.
Interstate 40 runs from Barstow, California, to Wilmington, North Carolina, and follows or closely parallels long sections of the former Route 66 corridor in the Southwest. In places, the interstate was built near the older highway; in others, it bypassed Route 66 communities entirely.
The relationship is especially visible in Arizona, New Mexico, Texas, and Oklahoma. Businesses that depended on through traffic often declined when motorists shifted to the faster, limited-access interstate. Some old alignments survived as local roads, frontage roads, or signed historic routes.
Interstate 40 did not replace every mile of Route 66. Other interstates, including Interstate 44 in Missouri and Oklahoma and Interstate 55 in Illinois, also absorbed traffic from different sections. Interstate 40 is the best-known successor across the western half of the historic corridor.