Radiator Springs was bypassed by Interstate 40 in 1961 in Pixar's Cars.
The date appears in the film's account of the town's decline. Radiator Springs once benefited from Route 66 traffic, but the construction of Interstate 40 redirected travelers away from the town. Sally Carrera explains that the bypass caused businesses to close and left the community isolated from the main flow of modern traffic.
Cars draws on the real history of Route 66, the highway established in 1926 and removed from the United States Numbered Highway System in 1985. Interstate highways often bypassed older communities, producing the kind of economic change dramatized by Radiator Springs.
The film is fictional, so Radiator Springs itself is not a real Arizona municipality. Its setting combines influences from real Route 66 communities, especially in Arizona and the American Southwest. The in-film date is 1961, not the later date when Route 66 was officially decommissioned.