Oops, sorry Analogman, I accidentally deleted your comment about this being a very narrow track that is only .75 miles long and suggesting it may be a bicycle track.
Acctually I did find reference to a bicycle test track in this area so I thnk you are correct.
Anonymous
@ 2008-07-01 14:25:54
It is a test track for a proposed "People Mover" autonomous transit system formerly under development by Otis Transportation Technology Division (TTD) in the mid- to late 1980s near the Denver area. It has been abandoned since the early 1990s.
Info Requested, Raceways - Test Tracks 
Acctually I did find reference to a bicycle test track in this area so I thnk you are correct.