Mentioned-only unmarked location
The I-40 or Interstate 40 is a freeway in the former United States of America. It was used to serve vacationers and commuters alike before the Great War. By 2281, Caesar's Legion has used the old highway to transport its legionaries and supplies as well as using it to display crucified prisoners and slaves such as the Twisted Hairs along it in the areas the Legion controls.
The I-40 connects many territories together and is a major trade route for caravans. It starts in North Carolina and goes through Tennessee, Arkansas, Oklahoma, Texas, New Mexico, Flagstaff in Arizona as well as intersects with Highway 93, twists around Bullhead City, and then enters California where it intersects with Highway 95 and then merges with I-15.
I-40 is mentioned only in Fallout: New Vegas.