Shenandoah Div Cab Signals (was Shenandoah Division Steam Locomotives)

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Fri Oct 25 21:46:39 EDT 2013

Thanks to Mr Jimmy Lisle for his link to the International Correspondence School 1930 volume on Automatic Train Control. This is the most lucid technical treatment I have yet read on the three competing types of "train control" in use in 1930: (1) the intermittent inductive type, (2) the axle current + loop current type, and (3) the 100 cycle Coded Track type. Unfortunately, the International Correspondence School volume does not indicate which of the three was installed on the Shenandoah Division.

So I dusted of a manuscript sent to me a year ago by Mr. Michael Savchak, E.E., P.E., of New York City. It is a pre-publication manuscript of a book he has in the works, and it contained a succinct paragraph giving just the information we needed to answer the question of what system of train control the N&W used on the Shenandoah Division. Mr. Savchak has given me permission to quote the following paragraph to the N&W List:


At the same time, the Norfolk and Western selected a three-speed pneumatic governor system for installation on its line between Hagerstown MD and Shenandoah VA. This installation used a 60-Hertz “loop” circuit. The locomotive cab signal used a backlit “H”, “M” and “L” for the three indications [high, medium and low speeds]. The second installation on the N&W was a two-speed electric governor system. This system was installed between Shenandoah VA and Roanoke VA. The first installation was made to be compatible with the second installation by the disabling of the governor’s high-speed contacts. The remaining features were the same, except that an electric governor was used in place of a pneumatic governor. The first installation on the N&W went into service on February 15, 1925 and the second installation went into service on January 1, 1927. The N&W discontinued the use of the speed control system in 1933, retaining cab signal only operations. The entire cab signal system on the N&W was removed from service in April 1956.


If you want to know the rather convoluted workings of the "loop type" of train control, read the I.C.S. volume which Mr. Lisle links !

It is indeed unfortunate that the N&W could not have waited a year to begin its installation. The N&W ended up buying the least efficient of the three competing systems, the axle current + loop current system. The axle current + loop current system, a Union Switch & Signal Co experiment, had been tested on the PRR's Sunbury & Lewistown Branch from 1924 to January 1926, at which time the apparatus was removed and retired. It was cumbersome and not very sophisticated, and was very quickly supplanted by the 100 cycle Coded Track system, which had first been tested in July 1926 (between Bryn Mawr and St. Davids on the PRR Philadelphia Division.) The 1926 tests of the new Coded Track system were so eminently successful that it quickly became the industry standard and the PRR, Long Island and New Haven began installation of the new technology in 1927, and further development of the old "axle current + loop current" system was discontinued in the industry. I cannot find reference in the literature to any other railroad having installed the "axle current + loop current" system, so the N&W may been the sole railroad on which it was used. It is unfortunate that none of the wayside or locomotive-born equipment was saved.

Mr. Savchak just sent me additional information which does not appear in his manuscript: Automatic Block Signals (Position Light) were first installed on the Shenandoah Division in connection with this cab signaling project - prior to that time, there had been no automatic block signals of any type. AC track and line relays were used throughout the entire installation. The signals were arranged in the APB (Absolute Permissive Block) style, and slide fences were installed where required. There were three interlockings within the Hagerstown-Shenandoah installation, and two interlockings on the Shenandoah-Roanoke portion. The C&O equipped four of its engines to run over the N&W between Glasgow and Loch Laird, 9 miles.

-- abram burnett

Sent to you from my Telegraph Key...

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