In Pixar's Cars, what real road inspired the film's setting and story?

U.S. Route 66 inspired the setting and story of Pixar's Cars.

The historic highway influenced Radiator Springs, a town whose fortunes decline after a faster interstate bypass removes through traffic. Pixar director John Lasseter and members of the creative team traveled along Route 66 while researching the film, meeting residents and documenting roadside architecture, landscapes, and attractions.

Route 66 once connected Chicago and Santa Monica across the United States. Although much of the original route was replaced or bypassed by the Interstate Highway System, many surviving communities preserve its history as a cultural road-trip landmark.

Interstate 40 is important inside the film because it is the bypass that harms Radiator Springs, but it is not the historic road that inspired the town. The answer is therefore Route 66, formally designated U.S. Route 66.