Interlocking

electronic interlockingrelay interlockinginterlockedmechanical interlockingelectro-mechanical interlockingtrack plan push button interlockingmechanical signal boxesroute relay interlockingelectro-mechanicaltrack plan interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings.wikipedia
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Railway signal

signalssignalsignalling
Interlocking ('controlled') signals are typically absolute, while automatic signals (i.e. those controlled through track occupancy alone, not by a signalman) are usually permissive.

John Saxby

Saxby and FarmerSaxby & FarmerSaxby
In June 1856, John Saxby received the first patent for interlocking switches and signals.
John Saxby (17 August 1821 – 22 April 1913) was an English engineer from Brighton, noted for his work in railway signalling and the invention of the interlocking system of points and signals.

Railway signalling

signallingrailway signalingblock signal
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings.
This required block signalling for all passenger railways, together with interlocking, both of which form the basis of modern signalling practice today.

Derail

derailerderailsautomatic derailer
The levers that operate switches, derails, signals or other appliances are connected to the bars running in one direction.

Railroad switch

pointsswitchcrossover
The levers that operate switches, derails, signals or other appliances are connected to the bars running in one direction.
Eventually, mechanical systems known as interlockings were introduced to make sure that a signal could only be set to allow a train to proceed over points when it was safe to do so.

Union Switch & Signal

Union Switch and SignalUnion Switch and Signal CompanyUS&S
Union Switch & Signal bought their company in 1882.
George Westinghouse founded Union Switch & Signal in 1881, consolidating the assets of the Union Electric Signal Company (founded by track circuit inventor William Robinson) and the Interlocking Switch & Signal Company (which had pioneered interlockings).

London and North Western Railway

LNWRLondon & North Western RailwayL&NWR
Preliminary latch locking became so successful that by 1873, 13,000 mechanical locking levers were employed on the London and North Western Railway alone.

Bricklayers Arms railway station

Bricklayers ArmsBricklayers' ArmsBricklayers Arms depot
The first mechanical interlocking was installed in 1843 at Bricklayers Arms Junction, England.
The signals and points were installed by Charles Hutton Gregory, and were the first to contain some elements of interlocking.

Centralized traffic control

CTCcentralised traffic controlCentralised Traffic Control (CTC)
Entrance-Exit Interlocking (NX) was the original brand name of the first generation relay-based centralized traffic control (CTC) interlocking system introduced in 1936 by GRS (represented in Europe by Metropolitan-Vickers).
The system consists of a centralized train dispatcher's office that controls railroad interlockings and traffic flows in portions of the rail system designated as CTC territory.

General Railway Signal

General Railway Signal CompanyGRS
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 Company (GRS, now a unit of Alstom, headquartered in Levallois-Perret, near Paris).

Junction (rail)

junctionrailway junctionrail junction
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings.

Relay logic

logic switchesrelayrelay circuits
Interlockings effected purely electrically (sometimes referred to as "all-electric") consist of complex circuitry made up of relays in an arrangement of relay logic that ascertain the state or position of each signal appliance.
This safety critical application uses interlocking to ensure conflicting routes can never be selected and helps reduce accidents.

Integrated Electronic Control Centre

IECCAutomatic Route SettingIntegrated Control Centre
Whereas before technologies such as NX and Automatic Route Setting required racks and racks of relays and other devices, solid state software based systems could handle such functions with less cost and physical footprint.
From the start, they controlled Solid State Interlockings (SSIs), a software version of the traditional relay interlocking, but existing relay interlockings may also be controlled from an IECC.

Signalling control

signal boxsignalboxinterlocking tower
In a move that was popular in Europe, the signalling for an entire area was condensed into a single large power signal box with a control panel in the operator's area and the equivalent of a telephone exchange in the floors below that combined the vital relay based interlocking logic and non-vital control logic in one place.
The technical apparatus used to control switches (points), signals and block systems is called interlocking.

Platform display

train describerdestination displaydynamic displays
Such advanced schemes would also include train describer and train tracking technologies.
The electric relay interlocking boxes were later replaced by electronic control boards where the train indication is just a text element on the video display.

Track (rail transport)

trackrailroad trackstracks
The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant.

United Kingdom

BritishUKBritain
Railway interlocking is of British origin, where numerous patents were granted.

Spuyten Duyvil, Bronx

Spuyten DuyvilSpuyten Duyvil, New YorkSpuyten Duyvil, Bronx, New York City
The first experiment with mechanical interlocking in the United States took place in 1875 by J. M. Toucey and William Buchanan at Spuyten Duyvil Junction in New York on the New York Central and Hudson River Railroad (NYC&HRR).

New York City

New YorkNew York, New YorkNew York City, New York
The first experiment with mechanical interlocking in the United States took place in 1875 by J. M. Toucey and William Buchanan at Spuyten Duyvil Junction in New York on the New York Central and Hudson River Railroad (NYC&HRR).

Harrisburg, Pennsylvania

HarrisburgHarrisburg, PAHarrisburg, Pa.
Toucey and Buchanan formed the Toucey and Buchanan Interlocking Switch and Signal Company in Harrisburg, Pennsylvania in 1878.

New York City Transit Authority

New York City TransitMTA New York City TransitNew York Transit Authority
The first important installations of their mechanism were on the switches and signals of the Manhattan Elevated Railroad Company and the New York Elevated Railroad Company in 1877-78.

Bound Brook, New Jersey

Bound BrookBound Brook BoroughBound Brook, NJ
An experimental hydro-pneumatic interlocking was installed at the Bound Brook, New Jersey junction of the Philadelphia and Reading Railroad and the Lehigh Valley Railroad in 1884.

Reading Company

Reading RailroadPhiladelphia and Reading RailroadReading
An experimental hydro-pneumatic interlocking was installed at the Bound Brook, New Jersey junction of the Philadelphia and Reading Railroad and the Lehigh Valley Railroad in 1884.

Lehigh Valley Railroad

Lehigh ValleyLVLehigh Valley Railway
An experimental hydro-pneumatic interlocking was installed at the Bound Brook, New Jersey junction of the Philadelphia and Reading Railroad and the Lehigh Valley Railroad in 1884.

Baltimore and Ohio Chicago Terminal Railroad

Chicago and Calumet Terminal RailwayChicago and Northern Pacific RailroadChicago Terminal Transfer Railroad
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.