@MartyE posted:
Really interesting. Never having been in the Chicago Union Station Interlocking Tower, is this the tower that controlled the south side, i.e. CB&Q etc., or the north side, i.e. C&NW and Milwaukee Road?
EDIT:
I have since found out that this is the Harrison Street Tower which controls the south portion of Chicago Union Station, for the station platforms to the CB&Q and PRR coach yards.