There is only one railway battalion remaining in the Army, and it's a reserve unit with headquarters in Milwaukee, WI. It has two companies directly assigned (1150th and 1152nd) and two that would be gained upon mobilization (1151st and 226th).
757th Transportation Battalion (Railway)
Milwaukee USARC
4850 West Silver Spring Drive
Milwaukee, WI 53218-3400
1150th Transportation Company (Railway Operating)
Phillip H. Sheridan USARC
3155 Blackhawk Drive
Fort Sheridan, IL 60037-1289
Det 1
Granite City USARC
Building 331
1230 First Street
Granite City, IL 62040-1801
1151st Transportation Company (Railway Operating)
Adrian B. Rhodes AFRC
2144 Lake Shore Drive
Wilmington, NC 28401-7297
Det 1
Blue Grass Army Depot USARC
2091 Kingston Highway
Richmond, KY 40475-5001
Det 2
Military Ocean Terminal Sunny Point
Southport, NC 28461-7800
1152nd Transportation Company (Railway Operating)
Milwaukee USARC
4850 West Silver Spring Drive
Milwaukee, WI 53218-3400
Det 1
Fort McCoy Complex
2010 South 8th Street
Fort McCoy, WI 54656-5136
226th Transportation Company (Railway Operating)
Westover Air Reserve Base
Chicopee, MA 01022
Whether or not the unit would actually be mobilized would depend upon a number of factors, such as the existence of an actual mission for the unit that could not be accomplished with personnel already available, the readiness level of the unit itself, etc.