Additional bus companies, listed as existing during additional years or decades, are mentioned in old City Directories, and in the WPA American Guide Series of state guidebooks.
Suburban and interurban bus companies listed in the Russell's Official National Motor Coach Guide, which was primarily a resource for intercity bus lines.
Colorado Motorway (to Longmont and Fort Collins, 1923-1975)
Bussard Taxi & Bus Service - served Englewood, Ft. Logan, Lakewood, Westwood.
Denver & South Platte Transportation Co. - certified 1926, served Littleton and Englewood.
Greeley-Longmont Motor Way - no further information.
Gilpin County Bus & Freight Line - served Denver, Black Hawk, Central City, Russell Gulch, Hiedi Chalet, Golden.
Rocky Mountain Motor Co. - existed in 1940's and 1950's.