Editing Interlocking (section)

==History==
Railway interlocking is of [[United Kingdom|British]] origin, where numerous patents were granted. In June 1856, [[John Saxby]] received the first patent for interlocking switches and signals.<ref>{{cite journal|title=Death of John Saxby|journal=Railway Age Gazette|volume=54|issue=20|page=1102|publisher=Simmons-Boardman Publishing Corporation|date=26 May 1913|oclc=15110423}}</ref><ref name="Solomon 2003">{{cite book |last=Solomon |first=Brian |title=Railroad Signaling |date=2003 |publisher=MBI Publishing Company |location=St Paul, Minnesota |isbn=978-0-7603-1360-2 |oclc=52464704}}</ref>{{rp|23-24}} In 1868, Saxby (of Saxby & Farmer)<ref>The first manufacturer of signal equipment, the predecessor of [[Westinghouse Brake and Signal Company Ltd]], and today’s [[Westinghouse Rail Systems]], Ltd. (headquartered in [[Chippenham, Wiltshire]])</ref> was awarded a patent for what is known today in North America as “preliminary latch locking”.<ref>{{cite patent|country=US|number=80878|gdate=11 August 1868|title=Improved Switch and Signal|invent1=John Saxby|invent2=John Stinson Farmer|status=patent}}</ref><ref name=r_age_gazette_1916_landmarks>{{cite journal|title=Landmarks in Signaling History|journal=Railway Age Gazette|date=28 July 1916|volume=61|issue=4|page=161|publisher=Simmons-Boardman Publishing Corporation}}</ref> Preliminary latch locking became so successful that by 1873, 13,000 mechanical locking levers were employed on the [[London and North Western Railway]] alone.<ref name=r_age_gazette_1916_landmarks/><ref name=elecinterhbook/>

The first experiment with mechanical interlocking in the United States took place in 1875 by J. M. Toucey and William Buchanan at [[Spuyten Duyvil, Bronx|Spuyten Duyvil]] Junction in [[New York City|New York]] on the [[New York Central and Hudson River Railroad]] (NYC&HRR).<ref name=r_age_gazette_1916_landmarks/><ref name=elecinterhbook>{{cite book|author=General Railway Signal Company|title=Electric Interlocking Handbook|url=https://archive.org/details/electricinterlo00cartgoog|date=1913|editor1-last=Sperry|editor1-first=Henry M.|publisher=General Railway Signal Company|location=Rochester, New York|pages=[https://archive.org/details/electricinterlo00cartgoog/page/n117 5]–12|oclc=3527846}}</ref><ref name=calvert>{{cite web|last=Calvert|first=J. B.|title=Toucey and Buchanan Interlocking|url=http://mysite.du.edu/~etuttle/rail/tandb1.htm|work=Railways: History, Signalling, Engineering|access-date=28 December 2011|url-status=live|archive-url=https://web.archive.org/web/20120423021307/http://mysite.du.edu/~etuttle/rail/tandb1.htm|archive-date=23 April 2012}}</ref> At the time, Toucey was General Superintendent and Buchanan was Superintendent of Machinery on the NYC&HRR. Toucey and Buchanan formed the Toucey and Buchanan Interlocking Switch and Signal Company in [[Harrisburg, Pennsylvania]] in 1878. The first important installations of their mechanism were on the switches and signals of the [[New York City Transit Authority|Manhattan Elevated Railroad Company]] and the New York Elevated Railroad Company in 1877–78.<ref name=r_age_gazette_1916_landmarks/> Compared to Saxby's design, Toucey and Buchanans' interlocking mechanism was more cumbersome and less sophisticated, and so was not implemented very widely.<ref name=calvert/> [[Union Switch & Signal]] bought their company in 1882.<ref name=calvert/>

As technology advanced the railway signaling industry looked to incorporate these new technologies into interlockings to increase the speed of route setting, the number of appliances controlled from a single point and to expand the distance that those same appliances could be operated from the point of control. The challenge facing the signal industry was achieving the same level of safety and reliability that was inherent to purely mechanical systems. An experimental [[hydro-pneumatic]]<ref>A system whereby compressed water and air are used to transmit action from one end of a long tube to the other end. It can be effective, but it still qualifies as a mechanical system since the pressure is pre-loaded, and requires human action of the same sort that a pure mechanical system requires.</ref> interlocking was installed at the [[Bound Brook, New Jersey]] junction of the [[Reading Company|Philadelphia and Reading Railroad]] and the [[Lehigh Valley Railroad]] in 1884.<ref name=r_age_gazette_1916_landmarks/><ref name=elecinterhbook/> By 1891, there were 18 hydro-pneumatic plants, on six railroads, operating a total of 482 levers.<ref name=r_age_gazette_1916_landmarks/> The installations worked, but there were serious defects in the design, and little saving of labour was achieved.

The inventors of the hydro-pneumatic system moved forward to an electro-pneumatic system in 1891 and this system, best identified with the Union Switch & Signal Company, was first installed on the [[Chicago and Northern Pacific Railroad]] at its drawbridge across the [[Chicago River]].<ref name=elecinterhbook/> By 1900, 54 electro-pneumatic interlocking plants, controlling a total of 1,864 interlocking levers, were in use on 13 North American railroads. This type of system would remain one of two viable competing systems into the future, although it did have the disadvantage of needing extra single-use equipment and requiring high maintenance.<ref name=elecinterhbook/>

Interlockings using electric motors for moving switches and signals became viable in 1894, when [[Siemens]] in Austria installed the first such interlocking at [[Přerov]] (now in the Czech Republic).<ref name=lexikonstellwerke>[[Lexikon der gesamten Technik]], entry "Stellwerke"</ref> Another interlocking of this type was installed in [[Berlin-Westend station|Westend]] near [[Berlin]] in 1896.<ref name=berlinerstellwerke>{{cite web|title=Berliner Stellwerke|url=http://www.berliner-stellwerke.de/|access-date=24 November 2012|url-status=live|archive-url=https://web.archive.org/web/20121128151953/http://www.berliner-stellwerke.de/|archive-date=28 November 2012}}</ref> In North America, the first installation of an interlocking plant using electric switch machines was at [[Eau Claire, Wisconsin]] on the [[Chicago, St. Paul, Minneapolis and Omaha Railway]] in 1901, by [[General Railway Signal|General Railway Signal Company]] (GRS, now a unit of [[Alstom]], headquartered in [[Levallois-Perret]], near Paris).<ref name=elecinterhbook/> By 1913, this type system had been installed on 83 railroads across 35 US states and Canadian provinces, in 440 interlocking plants using 21,370 levers.<ref name=r_age_gazette_1916_landmarks/>