Thats a good question.
My thoughts are that if so, it was probably back east on the Pennsy's narrow gauge lines. The PRR used a "block limit" system for secondary tracks (ie: branch lines.) It was actually the forerunner of TWC, but used telephones. A block control station (under the dispatcher's control) handled part or all of the line and issued block cards over the phone which gave authority to go from point A to point D and pass control points (Block Limits) between. When arriving at point D, the train would stop and call in for another block permit to procede farther. At each station, siding, or control point, a "Wooden Operator" was erected .... simply a post with station sign and a signal lamp displaying red beside yellow, with the yellow closest to the main track. They marked the limits of each block. The block card specified that the train could pass listed block limit signals as though a clear were displayed. It also listed the points which they could pass without calling in to report clear of the block. It was still manual block, but a very interesting system.
I've never heard of anything like that in the west before TWC.
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