Historic U.S. Route 66 most strongly inspired the setting and road culture of Pixar's Cars.
The film's creators researched Route 66 and drew on its roadside businesses, landscapes, and communities. Radiator Springs reflects towns that once depended on travelers but were bypassed when faster interstate highways diverted traffic. The movie uses that history as the foundation for its story about forgotten places and the value of slowing down.
Route 66 originally connected Chicago and Santa Monica. It was established in 1926 and became famous through migration, tourism, popular music, and American road mythology. The route was removed from the U.S. Highway System in 1985, but many historic sections and attractions remain.
Cars does not portray one exact real town. Radiator Springs combines influences from several locations, especially in the American Southwest. This is why Route 66 is the best answer, while nearby fictional names such as Ornament Valley describe locations within the film's world rather than real highways.