Interstate 10 in Arizona 2013. The remainder of the old US 80 section was rebuilt to interstate standards, with completion in 2014. East of Tucson, I‑10 parallels and in some cases overlies old US 80 to Benson, and was originally co-signed as US 80 and SR 86. The section of I-10 from Valencia Road to Rita Road was the first construction project in the state of Arizona funded by the Federal Aid Highway Act of 1956. Construction began in 1957 and was completed in 1960. From Benson, the Interstate follows the Southern Pacific mainline east through Willcox and Bowie to New Mexico, rather than
U.S. Route 80 in Arizona was bypassed in 1956 to cross the Colorado River, while the later alignment continued straight ahead into California. Upon crossing the Colorado River to the Fort Yuma Indian Reservation, the older route was still in Arizona. Unlike most of the California and Arizona state border which resides along the Colorado River, the border temporarily cuts north here through the Reservation then east back to the Colorado. This places several acres of land on the western side of the river in Arizona. For a few hundred feet, the state border runs along the western shoulder of pre-1956 US 80. A short