Headshunt

A headshunt (or escape track in the United States) is a short length of track provided to release locomotives at terminal platforms, or to allow shunting to take place clear of main lines.

Platform track and run-round loop at Toyooka Station, Hyōgo, Japan, the terminus of the line from Miyazu

Terminal headshuntEdit

 
Principle of a terminal headshunt:
1. train arrives to the station
2. the engine is detached from the train and moves to the headshunt
3. operations are made to reverse the engine's running direction (shifting between cabs...)
4. the engine passes the cars using the passing loop
5. operations are made to reverse the engine's running direction (shifting between cabs...)
6. the engine goes back to the cars
7. operations are made to reverse the engine's running direction, couple the engine with the cars, and the train can move

A 'terminal headshunt' is a short length of track that allows a locomotive to uncouple from its train, move forward, and then run back past it on a parallel track. Such headshunts are typically installed at a terminal station to allow the locomotive of an arriving train to move to the opposite end of (in railway parlance, 'run around') its train, so that it can then haul the same train out of the station in the other direction (assuming, of course, that it is a locomotive equipped to run in either direction; for older, one-way equipment such as steam locomotives and cab unit locomotives, a wye or turntable needs to be provided to physically turn the engine around, as well as a run-around track).

Reversing headshuntEdit

 
Melbourne University tram stop has three reversing headshunts in succession, between the two running lines.

Found primarily on metro systems, rapid transit light rail networks, and tramways, a 'reversing headshunt' allows certain trains or trams to change direction, even on lines with high traffic flow, whilst others continue through the station. Typically there will be two running lines, one for each direction of travel, and the headshunt will be positioned between the two running lines, linked to both by points. Although most trains will pass through the station and continue in the same direction, an individual train may be directed into the reversing headshunt, before exiting onto the other running line, in the opposite direction of travel. This procedure allows a greater frequency of trains on a city-centre section of the line, and reduced frequency on the suburban sections, by allowing certain trains to shuttle back and forth only on the city centre part, using the reversing headshunts to change direction within the flow of trains.

Shunting neckEdit

The term headshunt may also refer to shunting neck or 'shunt spur': a short length of track laid parallel to the main line for the purpose of allowing a train to shunt back into a siding or rail yard without occupying the main running-line.

Run roundEdit

 
Diagram of a headshunt and run round loop

A run round loop (or run-around loop) is a track arrangement that enables a locomotive to attach to the opposite end of the train. It is commonly used to haul wagons onto a siding, or at a terminal station to prepare for a return journey.[1] This process is known as "running round a train".[2]

Although a common procedure for passenger trains when the majority of them were locomotive-hauled, the maneuver is now becoming rarer on public service railways.[citation needed] Increased use of multiple unit and push-pull passenger services avoids the requirement for dedicated track and the need for railway staff to detach and reattach the locomotive at track level.[citation needed] However, on heritage railways run-round loops are still usually more or less necessary at each end of the running line, partly because train services are usually locomotive-hauled, and partly because the run-round operation gives added interest to visitors. This practice is still very common on Intercity services in Victoria, Australia.

Runaround tracks are used in freight rail service in order to back cars into spurs or to change directions to keep the locomotive at the front of the train for transport. In this case the runaround track must be as long as the longest set of cars that would be pulled. The locomotive leaves the cars on the runaround track or the main line, goes around, and hooks up to the other end of the train. It can then reverse the cars into a spur.

ExamplesEdit

Stations which used to have run-rounds include:

Stations which still have run-rounds include:

No loopEdit

If a terminal station has or no longer has a run-round loop, trains are restricted to multiple units or Top and Tail trains.

Relay enginesEdit

Sometimes a terminal station has no run-round loops, the absence of which is overcome by coupling a relay engine to the rear to power the next out bound trip. The original engine of the arriving train shunts to the relay engine siding where it awaits the arrival of the second train, and so on. Examples in steam days include Fenchurch Street and Kingsgrove.

ReferencesEdit

  1. ^ Jackson, Alan A. (2006). The Railway Dictionary (4th ed.). Sutton Publishing Ltd. p. 298. ISBN 0-7509-4218-5.
  2. ^ Ellis, Iain (2006). Ellis' British Railway Engineering Encyclopaedia. Lulu.com. p. 307. ISBN 978-1-8472-8643-7.