Passing loop
Encyclopedia
A passing loop is a place on a single line
railway or tramway, often located at a station, where trains or trams in opposing directions can pass each other. Train
s/tram
s in the same direction can also overtake, providing that the signalling
arrangement allows it. A passing loop is double ended and connected to the main track at both ends, though a dead end siding, which is much less convenient, can be used. A similar arrangement is used on the gauntlet track of cable railway
s and funicular
s, and in passing places on single-track roads.
Ideally, the loop should be longer than all trains needing to cross at that point. If one train is too long for the loop it must wait for the opposing train to enter the loop proceeding, taking a few minutes. Ideally, the shorter train should arrive first and leave second. If both trains are too long for the loop, time-consuming "see-sawing" (or "double saw-by") operations are required for the trains to cross.
On railway systems that use platforms
for passengers to board and disembark trains, especially high level platforms, platforms may be provided on both main and loop tracks or just either the main or loop track.
The main line has straight track, while the loop line has low speed turnouts at either end. If the station has only one platform, then it is usually located on the main line.
If passenger trains are relatively few in number, and the likelihood of two passenger trains crossing each other low, the platform on the loop line may be omitted.
A possible advantage of this layout is that trains which wish to pass straight through the station can do so uninterrupted (they do not have to reduce their speed to pass through the curve).
Since there is only one passenger platform, it is not convenient to cross two passenger trains.
Trains take the left-hand track (for example) in their direction of running. Low speed turnouts restrict the speed in one direction. Two platforms are needed and they can be island platform
or two side platforms. With an Up and Down loop, overtaking is not normally possible as some of the necessary signals are absent.
Crossing loops using Up and Down Working are very common with British practice. For one thing, there are fewer signals if the tracks in the station are signalled for one direction only, and also there is less likelihood of a collision caused by signalling a train onto the track belonging to the opposing train.
The speed restriction in one direction can be eliminated with higher speed turnouts, but this may require power operation as the longer and heavier high speed turnouts may be beyond the capability of manual lever operation.
the crossing loop had no platform, and as freight trains became longer it became inadequate to hold them. It has now been removed and passenger trains now cross using a short siding past the platform. Long freight trains do not need to cross each other here, while freight trains can cross passenger trains waiting in that short siding provided that the freight train arrives second and leaves first.
Molong used to have a short loop, but this was replaced by a long stretch of a former branch line which is a dead-end siding.
Berry
has had its short loop removed, and an even shorter dead-end siding substituted.
In the AusLink
project for the Junee to Melbourne
line, roughly every other section of single line will be duplicated to provide so-called passing lanes. About 220 km of the 450 km line will be duplicated.
In Sweden
, the passing loops are generally 750 m long, made for cargo trains. Passenger trains are usually much shorter, at least on most single track lines, less than 200 m. The signalling system now allows two passenger trains to cross without stopping, but one has to slow down to 40 km/h, because of the limited length of the loop and the sharp curves in the switch points.
For Norway
an investigation has been made about future high speed railways, using 250 km/h as cruise speed. The most promising link would be a new Oslo-Trondheim railway, which is suggested to be single track along a 370 km long route. It is suggested to have about 15 km long passing loops, more like 15 km double track, located about 80 km apart. This would enable passing in 160 km/h, but there could be only one train per hour per direction on the rail line. See also High-speed rail in Norway
.
policy generally, overlaps of about 500m and 200m respectively, overlaps are provided.
ed with home signals cleared by the approaching train. Some loops have the points in and out of the loop operated manually, albeit more recent examples have so-called self restoring switches that allow trains to exit a loop without needing to change the points.
Other forms of remote operation included Centralized traffic control
, where a train controller changes points and signals from a remote office; and driver operated points, which enable train crews to use a radio system to set the points from a distance.
One change would be to include runaway catchpoints on the downhill end, such as at Tumulla
.
One oddity was Dombarton, New South Wales in Australia
, where the crossing loop built to divide a long single line
section on an extreme 1 in 30 (3.3%) gradient. The "loop" was built as a miniature zig-zag with a single track lower switchback on one side and a double track upper switchback on the other side, with a dive tunnel under the through track connecting the two.
A refuge loop built on the ruling grade on Cowan bank
proved to be unworkable as the refuged train could not restart. This lesson was learned at Dombarton, where the uphill trains restart from level track. A refuge siding at Razorback
halfway up the ruling grade climb from Fish River
to Cullerin
also allowed trains to restart from level track.
A crossing loop on steep gradient may have catchpoints on the downhill end to reduce the impact of runaways.
. Train lengths are now as much as 1800 m.
See Longest trains
.
integer intervals along the track by travel time. The longest section between successive crossing loops will, like the weakest link in a chain, determine the overall line capacity.
Single track (rail)
A single track railway is where trains in both directions share the same track. Single track is normally used on lesser used rail lines, often branch lines, where the traffic density is not high enough to justify the cost of building double tracks....
railway or tramway, often located at a station, where trains or trams in opposing directions can pass each other. Train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...
s/tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
s in the same direction can also overtake, providing that the signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
arrangement allows it. A passing loop is double ended and connected to the main track at both ends, though a dead end siding, which is much less convenient, can be used. A similar arrangement is used on the gauntlet track of cable railway
Cable railway
A cable railway is a steeply graded railway that uses a cable or rope to haul trains.-Introduction:...
s and funicular
Funicular
A funicular, also known as an inclined plane or cliff railway, is a cable railway in which a cable attached to a pair of tram-like vehicles on rails moves them up and down a steep slope; the ascending and descending vehicles counterbalance each other.-Operation:The basic principle of funicular...
s, and in passing places on single-track roads.
Ideally, the loop should be longer than all trains needing to cross at that point. If one train is too long for the loop it must wait for the opposing train to enter the loop proceeding, taking a few minutes. Ideally, the shorter train should arrive first and leave second. If both trains are too long for the loop, time-consuming "see-sawing" (or "double saw-by") operations are required for the trains to cross.
On railway systems that use platforms
Railway platform
A railway platform is a section of pathway, alongside rail tracks at a train station, metro station or tram stop, at which passengers may board or alight from trains or trams. Almost all stations for rail transport have some form of platforms, with larger stations having multiple platforms...
for passengers to board and disembark trains, especially high level platforms, platforms may be provided on both main and loop tracks or just either the main or loop track.
Main and loop
If passenger trains are relatively few in number, and the likelihood of two passenger trains crossing each other low, the platform on the loop line may be omitted.
Platform road and through road
The through road has straight track, while the platform road has low speed turnouts at either end.A possible advantage of this layout is that trains which wish to pass straight through the station can do so uninterrupted (they do not have to reduce their speed to pass through the curve).
Since there is only one passenger platform, it is not convenient to cross two passenger trains.
Up and Down working
Island platform
An island platform is a station layout arrangement where a single platform is positioned between two tracks within a railway station, tram stop or transitway interchange...
or two side platforms. With an Up and Down loop, overtaking is not normally possible as some of the necessary signals are absent.
Crossing loops using Up and Down Working are very common with British practice. For one thing, there are fewer signals if the tracks in the station are signalled for one direction only, and also there is less likelihood of a collision caused by signalling a train onto the track belonging to the opposing train.
The speed restriction in one direction can be eliminated with higher speed turnouts, but this may require power operation as the longer and heavier high speed turnouts may be beyond the capability of manual lever operation.
Dead-end siding
It is possible to cross trains at stations equipped with only a siding. At BomboBombo railway station, New South Wales
Bombo is a CityRail railway station on the South Coast railway line. The station has 1 side platform, but has a platformless crossing loop and an extra siding, both of which are often used for passing freight trains. The station serves the adjacent beach, Bombo Beach, and the suburb of North Kiama...
the crossing loop had no platform, and as freight trains became longer it became inadequate to hold them. It has now been removed and passenger trains now cross using a short siding past the platform. Long freight trains do not need to cross each other here, while freight trains can cross passenger trains waiting in that short siding provided that the freight train arrives second and leaves first.
Molong used to have a short loop, but this was replaced by a long stretch of a former branch line which is a dead-end siding.
Berry
Berry, New South Wales
Berry is a small Australian town in the Shoalhaven region of the NSW South Coast in the state of New South Wales, located south of the state capital, Sydney. The indigenous people of the area were the Wodi Wodi people. In the 1810s, George William Evans, Government Surveyor, reported on the Berry...
has had its short loop removed, and an even shorter dead-end siding substituted.
Simultaneous crosses and passing lanes
If a crossing loop is several times the length of the trains using it, and is suitably signalled, then trains proceeding in opposite directions can pass (cross) each other without having to stop or even slow down. This greatly reduces the time lost by the first train to arrive at the crossing loop for the opposing train to go by. This system is also referred to as a dynamic loop.In the AusLink
AusLink
AusLink was an Australian Government land transport funding program, established in June 2004 and administered by the Department of Transport and Regional Services. In 2009 it was replaced with the Nation Building Program under the Nation Building Program Act 2009...
project for the Junee to Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...
line, roughly every other section of single line will be duplicated to provide so-called passing lanes. About 220 km of the 450 km line will be duplicated.
In Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, the passing loops are generally 750 m long, made for cargo trains. Passenger trains are usually much shorter, at least on most single track lines, less than 200 m. The signalling system now allows two passenger trains to cross without stopping, but one has to slow down to 40 km/h, because of the limited length of the loop and the sharp curves in the switch points.
For Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
an investigation has been made about future high speed railways, using 250 km/h as cruise speed. The most promising link would be a new Oslo-Trondheim railway, which is suggested to be single track along a 370 km long route. It is suggested to have about 15 km long passing loops, more like 15 km double track, located about 80 km apart. This would enable passing in 160 km/h, but there could be only one train per hour per direction on the rail line. See also High-speed rail in Norway
High-speed rail in Norway
Currently, the only high-speed rail in Norway, on the railways of Norway is on Gardermobanen, a 60 kilometer line between Oslo Central Station and Eidsvoll via Oslo Airport. The main service on this route is Flytoget, commuting between Oslo Airport and the metropolitan areas of Oslo at speeds of up...
.
Overlaps
Since space (length) is short, crossing loops do not normally have an overlap (safety margin) between the starting signals and the end of the double line. With the passing lanes and with the new ARTCARTC
ARTC may refer to:* Army Recruit Training Centre * Atlanta Radio Theatre Company, American theatre troupe* Australian Rail Track Corporation, government-owned corporation...
policy generally, overlaps of about 500m and 200m respectively, overlaps are provided.
Automatic operation
Many crossing loops are designed to operate automatically in an unattended mode. Such loops may be track circuitTrack circuit
A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...
ed with home signals cleared by the approaching train. Some loops have the points in and out of the loop operated manually, albeit more recent examples have so-called self restoring switches that allow trains to exit a loop without needing to change the points.
Other forms of remote operation included Centralized traffic control
Centralized traffic control
Centralized traffic control is a form of railway signalling that originated in North America and centralizes train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that...
, where a train controller changes points and signals from a remote office; and driver operated points, which enable train crews to use a radio system to set the points from a distance.
Gradients
The design of crossing loops may have to be modified where there are severe gradients that make it difficult for a train to restart from a stationary position, or where the terrain is unsuitable for a normal loop.One change would be to include runaway catchpoints on the downhill end, such as at Tumulla
Tumulla railway station, New South Wales
-Overview:The loop opened in 1910, and was signalled for Up and Down Working. The loop was about 400m long.Because of the steep grades, there was a safety siding at the down hill end of the up loop in case of runaways....
.
One oddity was Dombarton, New South Wales in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, where the crossing loop built to divide a long single line
Single track (rail)
A single track railway is where trains in both directions share the same track. Single track is normally used on lesser used rail lines, often branch lines, where the traffic density is not high enough to justify the cost of building double tracks....
section on an extreme 1 in 30 (3.3%) gradient. The "loop" was built as a miniature zig-zag with a single track lower switchback on one side and a double track upper switchback on the other side, with a dive tunnel under the through track connecting the two.
A refuge loop built on the ruling grade on Cowan bank
Cowan Bank
-Overview:The Cowan Bank is a 8.6 km double-track section of standard gauge railway line between Cowan railway station 48.8 km north of Sydney, New South Wales, Australia and Hawkesbury River railway station 57.4 km north of Sydney...
proved to be unworkable as the refuged train could not restart. This lesson was learned at Dombarton, where the uphill trains restart from level track. A refuge siding at Razorback
Razorback
Razorback is an Americanism, loosely applied to any type of feral pig or wild boar in North America. The term has also appeared in Australia, to describe said animals in that country.-Introduction to the Americas:...
halfway up the ruling grade climb from Fish River
Fish River (New South Wales)
- Rivers :There are two rivers in New South Wales called the Fish River.The Fish River rises on the plateau south east of Oberon, New South Wales, and flows generally to the north-west, becoming the main headwater of the Macquarie River just east of Bathurst, New South Wales. There is a reservoir...
to Cullerin
Cullerin, New South Wales
Cullerin is a small township in the Southern Tablelands of New South Wales, Australia in Upper Lachlan Shire. It is located on the Old Hume Highway and Main South railway line in southern New South Wales, Australia. The railway station opened in 1880 and closed in 1973.- Transport :Cullerin is at...
also allowed trains to restart from level track.
A crossing loop on steep gradient may have catchpoints on the downhill end to reduce the impact of runaways.
Train length
Since central operation of the points and signals from a single signal box is convenient, and since there are practical limits for the distance to these points and signals, crossing loops can have a system-wide effect on train sizes. In New South Wales, mechanical operation of points and signals limited train lengths in the steam era to about 400 m, which was only eased with the introduction of power operated points and centralized traffic controlCentralized traffic control
Centralized traffic control is a form of railway signalling that originated in North America and centralizes train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that...
. Train lengths are now as much as 1800 m.
See Longest trains
Longest trains
Conventional freight trains can average nearly 2,000 metres. Freight trains with a total length of three or four times that average are possible with the advent of DPUs , or additional locomotive engines between or behind long chains of freight cars...
.
Line capacity
Line capacity is partly determined by the distance between individual crossing loops. Ideally these should be located at inverseMultiplicative inverse
In mathematics, a multiplicative inverse or reciprocal for a number x, denoted by 1/x or x−1, is a number which when multiplied by x yields the multiplicative identity, 1. The multiplicative inverse of a fraction a/b is b/a. For the multiplicative inverse of a real number, divide 1 by the...
integer intervals along the track by travel time. The longest section between successive crossing loops will, like the weakest link in a chain, determine the overall line capacity.
Short loops
It is best if all crossing loops are longer than the longest train. Two long trains can cross at a short loop using a slow so-called see-saw process.Double lines
Overtaking sidings or loops can also be provided on double lines, one on each side, and these can be called Refuge Sidings which are deadended or Refuge Loops as the case may be.Accidents at crossing loops
- Casey JonesCasey JonesJohn Luther Jones was an American railroad engineer from Jackson, Tennessee, who worked for the Illinois Central Railroad...
(Vaughan, MississippiVaughan, MississippiVaughan is an unincorporated community in Yazoo County, Mississippi, United States. It is 32 miles from the state capital of Jackson and 12 miles east of Benton...
) - The legendary train driver (U.S.: engineer) Casey JonesCasey JonesJohn Luther Jones was an American railroad engineer from Jackson, Tennessee, who worked for the Illinois Central Railroad...
was killed in an accident in 1900 involving trains too long to cross at a passing loop. The trains trying to cross were occupying both the main and loop tracks, and in addition, the train doing the see-saw was standing outside station limits. Jones was traveling fast in order to make up lost time, and could not stop in time to avoid a collision. He was able to slow his train from an estimated 75 mph (120.7 km/h) to an estimated 35 mph (56.3 km/h) at the time of collision; none of the passengers on Jones' train were seriously injured, and Jones was the only fatality.
- Exeter crossing loop collisionExeter crossing loop collisionThe Exeter crossing loop collision was a railway accident that occurred between the Temora Mail Train and a goods train at Exeter railway station, New South Wales, on 13 March 1914. At that time the main line was a single track, with a crossing loop and a down refuge siding at Exeter.- Events...
(Exeter, Australia) - occurred at Exeter railway station in New South Wales, 1910s, in fog; one train too long for loop.
- Geurie crossing loop collisionGeurie crossing loop collisionThe Geurie crossing loop collision occurred on the night of 23 August, 1963. Geurie is located between Orange, New South Wales and Dubbo.- Events leading up to the Accident :...
(Geurie, Australia) - train in loop standing foul of main line, causing collision.
- Hines Hill train collisionHines Hill train collisionThe Hines Hill train collision occurred on the Eastern Goldfields Railway on 14 January 1996 at Hines Hill, Western Australia. Two trains entered a crossing loop simultaneously in opposing directions, although signals at the exit from the crossing loop were correctly showing red for...
(Hines Hill, Australia)
- Zanthus train collisionZanthus train collisionThe Zanthus train collision occurred at a crossing loop on the Trans-Australian Railway between Perth to Sydney on 18 August 1999. It is located east northeast of Perth and east of Kalgoorlie in Western Australia, on the Nullarbor Plain.-Incident:...
(Zanthus, Australia) - co-driver operated loop points prematurely.
- Dugald rail accident (Dugald, ManitobaDugald, ManitobaDugald is a community in Manitoba, Canada, 22 km east of Winnipeg. It was the site of a railway accident in 1947.It is located in the rural municipality of Springfield.Dugald is the birthplace of former NHL goaltender Trevor Kidd....
)
Other names
- crossing loop or crossing place
- passing siding (US)
- refuge loop or siding - used on double trackDouble trackA double track railway usually involves running one track in each direction, compared to a single track railway where trains in both directions share the same track.- Overview :...
lines - SpiralsSpiral (railway)A spiral is a technique employed by railways to ascend steep hills.A railway spiral rises on a steady curve until it has completed a loop, passing over itself as it gains height, allowing the railway to gain vertical elevation in a relatively short horizontal distance...
are sometimes called loops. - Balloon loopBalloon loopA balloon loop or turning loop allows a rail vehicle or train to reverse direction without having to shunt or even stop. Balloon loops can be useful for passenger trains and unit freight trains, such as coal trains....
s are sometimes called loops.
See also
- Lists of rail accidents
- Run-around loop
- Siding (rail)
- Glossary of North American railway terminology