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 ?
Rails serve as traction current conductors as well as track circuit conductors.
This triggered three track circuit failures, causing the signaller to receive a false indication the section of track was occupied by a train.
That meant it was necessary to manually monitor the condition of every track circuit, on-site, with a digital multi-meter, a costly, time-consuming task with little scope for predictive maintenance.
THOUSANDS of Delhi Metro commuters had a harrowing experience on Monday as services on the busy Blue Line -- which connects Dwarka with Noida and Vaishali -- were affected for several hours due to a major technical snag in its track circuit.
In [5], a track circuit was digitally simulated via boundary-condition analysis, and the adaptability of ballastless track circuits was studied in [6].
The National Transportation Safety Board has already indicated that problems with Metro's track circuit equipment contributed to the crash outside of the Fort Totten rail station, preventing the automatic safety system from stopping the trains before they got too close.
It hasn't taken long for the 6-foot-3 Belton to make a name for himself on the scholastic track circuit.
Trains were disrupted by a track circuit failure between Moorfields and Liverpool Central.
A spokesman for Network Rail said: 'On December 31 we found one track circuit had been wired incorrectly.
That year turned out to be his best year on the track circuit.
The company today blamed heavy rain in three of the six months for causing track circuit failures leading to delays.