Business Loop I-70 - Golden, Denver, Aurora

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Following all of Colfax Avenue, Business Loop I-70 runs alongside U.S. 40 for its 27.47 mile route from Golden to Aurora, and with U.S. 287 east from Federal Boulevard and Sun Valley in Denver. The route is not acknowledged from signs at the west end with I-70, nor on I-25 or I-225. The Colorado Department of Transportation (CDOT) inventories Business 70 solely as U.S. 40 (Route 040C).

Colfax Avenue is named after Schyuler Colfax, an Indiana congressman who passed through Colorado in 1865 and later became Vice President under Ulysses S. Grant. If it were not named for Colfax, it would be 15th Avenue. According to the Denver Rocky Mountain News from June 19, 2000, Colfax Avenue is "the longest continuous commercial thoroughfare" in the United States.

Historically U.S. 36 also overlapped with U.S. 40 along Colfax Avenue. U.S. 36 later shifted onto an unmarked concurrency with I-70 and I-270.