That's the unit crest ("distinctive unit insignia" -- DUI) worn by the Transportation Center & School, formerly at Fort Eustis (now Joint Base Langley-Eustis) and now at Fort Lee, VA, where Transportation, Quartermaster, and Ordnance training has been consolidated.
I first saw this insignia in early 1975 when I was right out of basic training and assigned to the 1st Railway Detachment at Fort Eustis. My unit, however, didn't wear this insignia. Instead, we wore the TRADOC (Training & Doctrine Command) DUI seen here: Link Our shoulder patch was the diamond-shaped TC school insignia. I would have preferred to wear the TC&S insignia because it had railroad tracks on it. Unfortunately nothing we wore gave any hint that we were members of a railway unit.
By that point our little detachment was the last active duty rail unit in the Army and a year later our MOSs would be eliminated and limited only to the Army Reserve, and at the end of September 1978 the little 1st Rail Det disappeared for good.
Thanks to Greg for sending photo and question and for working on our Facebook page visit it and 'like' it today. https://www.facebook.com/militaryrailwayservice/