From ArborWiki

Switching yard on the Ann Arbor Railroad next to Ferry Field, near where it crosses Hoover Avenue.

The yard was used for football special trains carrying fans from the north and south, per this account from rail historian Jim Sinclair:

According to an article that appears in an old AARRT&HA publication, the football specials started shortly after the turn of the century. The trains grew in popularity during the twenties and thirties and were still going quite strong into the late 50s and early 60s. The Ann Arbor also installed an APB (Automatic Permissive Block) signal system between Milan and Ferry during the early thirties to safely move the fleet of football specials to or from Ferry Yard. While most of the specials came out of Toledo, some also came out of Detroit on the Wabash and in fact, a connection at Milan in the northeast quadrant was appropriately and officially named, "The Football Wye."

A photo of the building in the yard once used for operations: http://www.flickr.com/photos/johnbaird/36196961/