Track Circuit

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Track Circuit


an isolated segment of a railroad line that is part of the railroad signaling system; track lines serve as current conductors in this circuit. These isolated railroad segments are called blocks. Blocks are track sensors that are tripped by the action of the wheels of the rolling stock, thus establishing a contact between the rolling stock and the control devices—the railroad switches and signals. When the track circuit is free of traffic, the current of the track battery passes through the track relay, whose contacts close the circuit for the green light signal. When the wheels of the rolling stock pass onto a track circuit, the track relay is shunted and the armature of the track relay drops, which results in a red or a red-yellow light signal.

In order to check that the track circuit is free of traffic, a signal current is sent through the circuit—direct currents and alternating currents are determined by the type of track circuit. Circuits that are normally closed and those that are normally open are determined by their operating principles. An operable track circuit is considered to be in a normal state when it is free of rolling stock.

When the track circuit is of a normally closed type, the current is sent continuously; thus, in addition to its basic functions, the circuit also checks the working order of the track devices, including the track line. When the track circuit is normally open, the track relay is usually not activated and does not check the working order of the circuit. Except in marshaling yards, only track circuits that are normally closed are used on railroad lines in the USSR.


Bryleev, A. M., A. V. Shishliakov, and Iu. A. Kravtsov. Ustroistvo i rabota rel’sovykh tsepei. Moscow, 1966.


References in periodicals archive ?
Track circuits detect the clear or occupied condition of a specific track section and therefore are very important in terms of rail traffic safety.
The upgrade includes the introduction of a new signalling system of 385 jointless track circuits to detect train position, maintain safe separation distances and deliver train headways capable of meeting the extremely demanding timetable.
The problem occurred due to damage or theft in the signalling cable measuring around 700 m connecting the track circuits to the junction box between the Pragati Maidan and Mandi House Metro stations on the up line ( towards Dwarka)," DMRC officer Anuj Dayal said.
Jointless track circuits (JTCs) are a key component of train control systems (TCSs) and are used for train detection.
Water built up in the morning causing electrical problems on the track circuits and at 1.
An Arriva Trains Wales spokesman said: "There was multiple signal failure [with] the track circuits that pass electricity through the rail and everything that tells signalmen where the trains are.
The track, one of the first such sites in the UK, will have three track circuits - novice, youth and adult.
The signals and communications program was designed to take electronics and electrical students from a common first-year grouping and funnel them into more specialized second-year streams, learning about power supply, relays, track circuits, switches, cross warning systems and other related items.
Virgin CrossCountry services from Liverpool had to be terminated at Stafford and trains from Preston were cancelled altogether after the signals and track circuits at Basford Hall, near Crewe, failed.
Contract notice: engineering of the security equipment at botev, kalofer, tuzha, sahrane, dunavtsi and cherganovo railway stations on the third main railway line - replacement of track circuits with axle counters.