From the outset, public road planners intended U.S. 66 to connect the main streets of rural and urban communities along its course for the most practical of reasons: most small towns had no prior access to a major national thoroughfare.

Commissioned in 1926, U.S. Route 66 was primarily designed as a "diagonal" connector to link the rural communities of the Midwest with the urban hubs of the West Coast. Unlike the more linear transcontinental trails that preceded it, Route 66 was built to provide farmers and small-town entrepreneurs in Illinois, Missouri, and Kansas a direct path to redistribute grain and produce to larger markets. Its specific path was chosen to be "all-weather," favoring a more temperate southern climate that stayed navigable during winter months when northern routes were blocked by snow. This made it a vital artery for the emerging trucking industry, which began to compete with the railroads for freight dominance. Later, during the Dust Bowl of the 1930s, the road took on a new social purpose as the "Mother Road," facilitating the migration of hundreds of thousands of people fleeing economic hardship for a better life in California. It also served a critical military function during World War II, moving troops and equipment to training bases in the Southwest.