 Before the formation of the United States Numbered Highways , the U.S. relied on an informal network of roads , organized by various competing interests , collectively called the auto trail system . The surveyors of most trails chose either South Pass in Wyoming or a southern route through New Mexico to traverse the Rocky Mountains . Both options were less formidable than the higher mountain passes in Colorado , but left the state without a transcontinental artery . When the planners of the Lincoln Highway also decided to cross the Rockies in Wyoming , officials pressed for a loop to branch from the main route in Nebraska , enter Colorado , and return to the main route in Wyoming . While the Lincoln Highway was briefly routed this way , the loop proved impractical and was soon removed . 
