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A single-track
railway Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
is a railway where
train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often ...
s traveling in both directions share the same track. Single track is usually found on lesser-used rail lines, often
branch line A branch line is a phrase used in railway terminology to denote a secondary railway line which branches off a more important through route, usually a main line. A very short branch line may be called a spur line. Industrial spur An industr ...
s, where the level of traffic is not high enough to justify the cost of constructing and maintaining a second track.


Advantages and disadvantages

Single track is significantly cheaper to build and maintain, but has operational and safety disadvantages. For example, a single-track line that takes 15 minutes to travel through would have capacity for only two trains per hour in each direction safely. By contrast, a double track with signal boxes four minutes apart can allow up to 15 trains per hour in each direction safely, provided all the trains travel at the same speed. This hindrance on the capacity of a single track may be partly overcome by making the track one-way on alternate days, if the single track is not used for public passenger transit. Long
freight train Rail freight transport is the use of railroads and trains to transport cargo as opposed to human passengers. A freight train, cargo train, or goods train is a group of freight cars (US) or goods wagons (International Union of Railways) haul ...
s are a problem if the passing stretches are not long enough. Other disadvantages include the propagation of delays, since one delayed train on a single track will also delay any train waiting for it to pass. Also, a single track does not have a "reserve" track that can allow a reduced capacity service to continue if one track is closed.


Single-track operations


Passing loops

If a single-track line is designed to be used by more than one train at a time, it must have
passing loop A passing loop (UK usage) or passing siding (North America) (also called a crossing loop, crossing place, refuge loop or, colloquially, a hole) is a place on a single line railway or tramway, often located at or near a station, where trains or ...
s (also called ''passing sidings'' or ''crossing loops'') at intervals along the line to allow trains running in different directions to pass each other. These consist of short stretches of double track, usually long enough to hold one train. The capacity of a single-track line is determined by the number of passing loops. Passing loops may also be used to allow trains heading in the same direction at different speeds to overtake. In some circumstances on some isolated
branch line A branch line is a phrase used in railway terminology to denote a secondary railway line which branches off a more important through route, usually a main line. A very short branch line may be called a spur line. Industrial spur An industr ...
s with a simple shuttle service (such as the
Abbey Line The Abbey Line, also called the St Albans Abbey branch line, is a railway line from Watford Junction to St Albans Abbey. The route passes through town and countryside in the county of Hertfordshire, just outside the boundaries of the Oyster C ...
in Great Britain or L202 railway in Croatia) a single-track line may work under the "one train working" principle without passing loops, where only one train is allowed on the line at a time.


Safety operations

On single-track lines with passing loops, measures must be taken to ensure that only one train in one direction can use a stretch of single track at a time, as
head-on collision A head-on collision is a traffic collision where the front ends of two vehicles such as cars, trains, ships or planes hit each other when travelling in opposite directions, as opposed to a side collision or rear-end collision. Rail transpor ...
s are a particular risk. Some form of signalling system is required. In traditional
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...
practice (and countries using British practice), single-track lines were operated using a token system where the train driver had to be in possession of a token in order to enter a stretch of single track. Because there was only one unique token issued at any one time for each stretch of single track, it was impossible for more than one train to be on it at a time. This method is still used on some minor lines but in the longest single-track lines in Britain (e.g. the
Highlands Highland is a broad term for areas of higher elevation, such as a mountain range or mountainous plateau. Highland, Highlands, or The Highlands, may also refer to: Places Albania * Dukagjin Highlands Armenia * Armenian Highlands Australia *Sou ...
of Scotland) this has been superseded by radio communication, known as
Radio Electronic Token Block Radio Electronic Token Block is a system of railway signalling used in the United Kingdom. It is a development of the physical token system for controlling traffic on single lines. The system is slightly similar to North American Direct Traffic ...
. In the early days of railways in North America it was common to rely upon simple timetable operation where operators knew where a train was scheduled to be at a particular time, and so would not enter a single-track stretch when they were not scheduled to. This generally worked but was inflexible and inefficient. It was improved with the invention of the telegraph and the ability to issue train orders.


Doubling and singling

Converting a single-track railway to double track is called duplication or doubling; converting double track to single track is known as singling. A double-track railway operating only a single track is known as single-line working.
Kirkby railway station Kirkby railway station is situated in Kirkby, Merseyside, England. The station is an interchange between Merseyrail services from Liverpool Central and Northern services from Manchester Victoria via Wigan Wallgate. It is situated 7.5 miles (12 ...
(until 1977) and
Ormskirk railway station Ormskirk railway station in Ormskirk, Lancashire, England, is a cross-platform interchange between Merseyrail services from Liverpool Central and Northern Trains services from Preston on the Ormskirk branch line, northeast of Liverpool. The st ...
(until 1970) were double-track railway, when they were converted into single-track railway with
cross-platform interchange A cross-platform interchange is a type of interchange between different lines at a metro (or other railway) station. The term originates with the London Underground; such layouts exist in other networks but are not commonly so named. In the U ...
.


New bike paths and railway corridors

Building bike trails on rail corridors has occurred in limited examples; however, developing rail rights of way for a bike trail can restrict a train corridor to a single track. Also reclaiming a railway corridor to use trains again limits the use of double tracks. The bike path is usually where the second track would be, and there may be fierce opposition by bikers and hikers. An example of a bike, single-track corridor is the E&N Railway in Victoria, Canada.


References


External links


rails to trails
{{Railway track layouts Railway line types