Comments from Graydon Meints: 4/14/2003: Most interlockings, originally, used pipes to move switches, derails, and semaphore arms. It was later that electric and pneumatic came into operation. I remember that Pearl Street in Jackson, Second Avenue in Grand Rapids, MA in Lansing, and North Lansing were electric. I think Sunnyside in Grand Rapids also was electric. There probably were others but these are the only ones I'm familiar with.
Distant signals in non-automatic block signal territory were always, to the very best of my knowledge, stationary and displayed the "caution" indication at all times. In ABS territory distant signals were an integral part of the ABS signal system and not a separately designated signal type.
The development of track circuitry and automatic signaling is fascinating. When you figure that all the different ABS signal indications stand on one thing--a train on a given track circuit--it is an ingenious system.
Station Approach Signals
Comments from Graydon Meints: 4/14/2003: The Michigan Central had a type of signal called "station semaphore" that was used to protect trains working at stations where there was limited view of the track by an approaching train. I'd have to look in an employee timetable of the 1950's--at which time they were still in use. I think that Middleville, Hastings, and Eaton Rapids had them. Mackinaw City had one for northward trains. There were others. When they were finally discontinued--in the 1950s--they were operated by trains occupying a track circuit. I'm sure that in earlier days they were manually operated, probably by a wire from some location that ran out to the signal. Sounds primitive by today's standards, but at the time they probably were state of the art and did protect switching movements. They supplemented the manual block system, but did not supersede it. The manual block system insofar as it applied to non-passenger-carrying trains provided a clear block indication only outside of yard limits. All second- and lower-class trains and extras had to move at restricted speed within yard limits. So they probably improved the movement of such trains to some extent.