In Pixar's Cars, Interstate 40 bypasses Radiator Springs and causes the town to lose passing travelers.
The film explains that Radiator Springs once prospered because Route 66 carried motorists through the community. When Interstate 40 opened nearby, drivers could pass the town more quickly without stopping, and local businesses declined.
This background gives the setting its historical identity. The town's residents preserve memories of the old road, while the newer interstate symbolizes the changes that left them behind. Lightning McQueen's detour reconnects him with that older roadside world.
Interstate 40 is sometimes confused with Route 66 because both roads are central to the town's history. Route 66 is the historic road through Radiator Springs; Interstate 40 is the newer bypass that redirects traffic away from it.