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The first interlocking machine is credited to Sir Charles Hutton Gregory who is also the inventor of the semaphore. His original installation at Bricklayers’ Arms Junction  in 1843 was the first time an “arrangement of switch, lock and signal appliances so interconnected that their movements must succeed each other in pre-determined order” was ever used. The signals were not interlocked to the position of the turnouts however, a significant flaw. English inventors soon embraced the concept and many competing designs were developed. At least a dozen English companies soon were producing mechanical plants and the need became ever greater as the safety at speed advantage of the interlocking machine statistically demonstrated.
In June, 1856 John Saxby patented a machine whereby the signals and the turnout points were interconnected in unimpeachable fashion. His newly patented invention was installed at the same Bricklayers’ Arms Junction and replaced the earlier Gregory device.
By 1863 Saxby had joined with John Stinson Farmer and together they developed a works near London to produce the patented devices invented by Saxby. By 1872 the work went world wide with a satellite plant opened in France.
Ashbel Welch, an American who was a principal with the Philadelphia and Trenton Railroad ordered an interlocking machine for “Top of the Hill”, a junction on his line near Trenton, NJ. The machine was S&F No. 905, protected by patent in 1867 and was a spring catch type. On December 7, 1870 the machine was placed in service. The interlocking revolution had begun in America.
John Toucey and William Buchanan who met during their service with the NYC&HR teamed up to produce their own machine and in 1874 they installed their first machine at Spuyten Duyvil Junction on the Hudson River Railroad. It replaced an English machine made by Joseph Brierly and Sons. The T&B machine was a hinge plate design and required depressing a foot treadle rather than a latch handle to affect a lever move.
George Westinghouse on May 1, 1880 formed the Union Switch & Signal Co. after acquiring patent rights to the S&F, T&B, Union Electric Signal and Jackson Manufacturing Co. The new US&SCo. was headquartered in Pittsburg, Pa. also Westinghouse’s home town.
John Taylor, of Piketon, Oh. had patented several devices for railway dispatching. He approached officials of the B&O Southwestern in 1889. The meeting ended with a promise by Taylor to design an electric interlocking system. He produced a prototype system and demonstrated it in Chicago in 1889. Deemed too lightweight for railroad use, his patron urged him to visit a mechanical plant in Indianapolis in 1890. Mr. Taylor returned to Clillichothe Ohio and built a new machine in the B&OSW shops. By 1891 it was installed  at east Norwood, Ohio. The nucleus for the General Railway Signaling Company had been formed. GRS was a merger between Taylor-Sergent, Hall and Pneumatic Signal Companies and was headquartered in Buffalo, NY., later moved to Rochester.
Johnson Signal Company of Rahway, NJ and Federal Signal Company of Troy, NY are two other companies who produced early interlocking machines of the vertical locking type.
Did railroads play favorites? You bet. The PRR for example had only one non-USSCo machine on the Fort Wayne Division at Indiana Harbor Canal Drawbridge in East Chicago, IN. A GRS searchlight installation in Plymouth and that was it for the FTW. The early TCS and Monon crossing were GRS products also on the PRR St. Louis Division most of the others being the Improved Saxby & Farmer or the ISF with S-8 electric levers in addition to the mechanical machine.
NYC favored the GRS machines. Do you think geography or familiarity  was the deciding factor?
 
WJ Mattes, Garrett, IN
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