I believe it was in 1956 that the NYC upgraded the Elkhart Branch (Air Line) between Jackson and Three Rivers via Homer and Union City. It was CTC with 60 MPH running, and most of the hot Detroit-Jackson-Chicago traffic was routed that way. Elkhart was a major classification yard and crew change point. A high-speed connecting track was installed at Three Rivers to head south to Elkhart. Later in the 80's under Conrail, the Elkhart Branch was downgraded (and eventually abandoned) and they started running the through traffic via Kalamazoo, around the connecting track at BO toward Three Rivers and then to Elkhart.