N&W's Last Semaphores on Main Lines?

[NW Mailing List]

Has anyone yet figured out when and where the semaphores made their last stands on N&W main lines, before being replaced with Position Light Signals ? 

I can understand that, coincident with the installation of CTC, PL's probably replaced semaphores. But there were many instances of N&W double track which was not operated as CTC, and those areas all received PL's at some point in time. 

Is there any paper evidence, or photographic evidence...? 

-- abram burnett 

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