From Trains Magazine:

Time has caught up with the famed “BO” tower in Kalamazoo this week. On Tuesday morning, signal crews working on Amtrak’s Michigan Line upgrades retired the 44-lever Saxby & Farmer interlocking machine, marking the end of the tower era in western Michigan.

For the time being, operators still work around the clock at BO, operating signals from a control panel in the tower. The signals will eventually be remote-controlled, once responsibility for MDOT’s Kalamazoo-Dearborn route is handed from Norfolk Southern’s dispatchers in Dearborn, Michigan to Amtrak’s train directors in Chicago.

The installation of the interlocking by Michigan Central, a New York Central affiliate, was approved by the Michigan Railroad Commission in January 1915, leaving BO’s original interlocking machine to end its service life just four months short of its centennial celebration.

The tower once controlled lines affiliated with the Grand Trunk Western, New York Central, and Pennsylvania, along with an interurban. Both of the lines remaining today were conveyed to Penn Central in 1968 and then split between Amtrak and Conrail in 1976. Norfolk Southern acquired both remaining Conrail routes in 1999, and then spun off the north-south alignment, the former Pennsylvania route, to Watco-owned Grand Elk Railroad in 2009. The state acquired the former New York Central route east of the tower in 2013 with NS retaining freight rights.

Amtrak and the state of Michigan are in the process of upgrading the Kalamazoo-Dearborn corridor for 110 mph speeds, which includes major track upgrades along with a complete replacement of the signal system to modern hardware that provides positive train control.