Railway Track Circuits

Track Circuits

Railway Track Circuits

1. Introduction
2. Components
3. Working
4. Do’s & Don’t
5. Other technology
6. Present era of technology
7. Conclusion

1. Track circuit is simple electrical device used to detect the Presence/Absence of train on the rails.
2. Track circuit is the one of the primary input for a signal interlocking plant.
3. The signal cannot be green while there is another train on track segment ahead.

Track Circuit

1. Battery.
2. Track Relay.
3. Adjustable resistance.
4. Insulated rail joints.

1. Gravity cells are used .

1. A relay is electrically operated switch.
2. The Relay switch connections are usually labelled common ,normally closed, normally open.


Adjustable Resistance
TRc – Track Lead Resistance at feed end
TRr – Track lead Resistance at Relay end
RT – Regulating Resistance
Rr – Rail Resistance (Rail joint Resistance)
RB – Ballast Resistance
TSR – Train Shunt Resistance

Insulated rail joints
1. Track circuit required insulated rail joint for isolating it the adjacent track circuit.

2. Nylon IRJ
3. Glued IRJ

Insulated rail joints


Track circuit bonding

Rail bond need to be provided on track circuit have point turnout them.

Track circuit bonding

Track circuit bonding



1. The portion of the Track which is to be Track circuited, is first provided with wooden or RCC sleepers and then the rails are insulated from the rest of the Track by the provision of Insulated rail joints.
2. At one end of the Track circuit feed is connected and at other end track relay is connected.
3. When the track portion is not occupied by trains, the fed is available for track relay and the relay is in energized condition.

When a train occupies the track circuit portion, the axel & wheels shunt the track much of the circuit current is passed through the wheels due to less resistive path and very less current is available for track relay, which is not sufficient enough to pick up the relay.

Simplified DC Track Circuit

Simplified Interlocking Relay Application



1. Those section of the track circuit in which occupation by a vehicle cannot be detected.
2. Curved track.
3. Cross.
4. Bridge .

Dead Section 1


Dead Section 1



1. Top up distilled water if the electrolyte level is low in batteries.
2. Change the relay which is due to for overhauling.
3. Replace the damaged and corroded bonding wires.
4. Do not Tilt the relay.

5. Do not Test the track circuit by shunting with a wire only.
6. Track circuit does not get shunted properly by vehicles.
7. Its working length is dependent on immunity of track relay.

1. AC Track circuit.
2. Audio Frequency Track circuit.
3. Axle Counter.







1. Indian Railways is installing a state-of-art technology along train tracks to detect of faults and defective parts in coaches, wagons and locomotives.
2. The new system, which uses high-speed infrared and digital cameras, will replace physical examination of the wagons by railway staff.
3. The project, which will be run as trial project will be installed at 10 locations at an estimated cost of 73 crore rupees in the first phase.


1. DC Track circuit are the simplest , least costly and most reliable type of track circuit.
2. Now a days for signalling purposes , trains are monitored automatically by means of TRACK CIRCUIT.
3. Track circuit play important role in stop accidents,traffic .


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