Single track (rail)
Encyclopedia
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 line
s, where the traffic density is not high enough to justify the cost of building double track
s.
Long freight train
s are a problem if there are not enough long passing stretches. Other disadvantages include the spread of delays, since if one train on a single track is delayed, any train waiting for it to pass also will be delayed etc. Also, single track does not have a "reserve" track that can allow a reduced capacity service to continue if one track is closed.
s (short stretches of double track) at intervals along the line to allow trains running in different directions to pass each other. Although in some circumstances (such as the Abbey Line in Great Britain) 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.
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
s are a particular risk. Some form of signalling system
is required. In traditional British
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 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. 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.
Some early wagonway
s were primarily single track with passing loops at frequent intervals. The crossing loops were arranged to be in line of sight of one another, so that drivers in one direction could see if vehicles in the opposing direction were already in the single line section. The single line sections needed to be straight, so the profile of the line tended to be a series of chords
rather than a smooth arc
.
.
Branch line
A branch line is 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...
s, where the traffic density is not high enough to justify the cost of building double track
Double track
A 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 :...
s.
Advantages and disadvantages
Single track is significantly cheaper to build, though it has a number of operational disadvantages. If the single track section is say 15 minutes long, then the line would have capacity for only two trains per hour in each direction. A double track typically can allow up to 15 trains per hour in each direction if signal boxes are 4 minutes apart. 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 transit.Long freight train
Freight train
A freight train or goods train is a group of freight cars or goods wagons hauled by one or more locomotives on a railway, ultimately transporting cargo between two points as part of the logistics chain...
s are a problem if there are not enough long passing stretches. Other disadvantages include the spread of delays, since if one train on a single track is delayed, any train waiting for it to pass also will be delayed etc. Also, 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
If a single track line is designed to be used by more than one train at a time, it will have passing loopPassing loop
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. Trains/trams in the same direction can also overtake, providing that the signalling arrangement allows it...
s (short stretches of double track) at intervals along the line to allow trains running in different directions to pass each other. Although in some circumstances (such as the Abbey Line in Great Britain) 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.
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
Head-on collision
A head-on collision is one where the front ends of two ships, trains, planes or vehicles hit each other, as opposed to a side collision or rear-end collision.-Rail transport:...
s are a particular risk. Some form of signalling system
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...
is required. In traditional British
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
practice (and countries using British practice), single track lines were operated using a token system
Token (railway signalling)
In railway signalling, a token is a physical object which a locomotive driver is required to have or see before entering onto a particular section of single track. The token is clearly endorsed with the name of the section it belongs to...
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 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. In the early days of railways in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
it was common to rely upon simple timetable operation
Train order
Train order operation, or more accurately Timetable and Train order operation, is a largely obsolete system by which the railroads of North America conveyed operating instructions before the days of centralized traffic control, direct traffic control, and the use of track warrants conveyed by radio...
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
Electrical telegraph
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages....
and the ability to issue train orders.
Some early wagonway
Wagonway
Wagonways consisted of the horses, equipment and tracks used for hauling wagons, which preceded steam powered railways. The terms "plateway", "tramway" and in someplaces, "dramway" are also found.- Early developments :...
s were primarily single track with passing loops at frequent intervals. The crossing loops were arranged to be in line of sight of one another, so that drivers in one direction could see if vehicles in the opposing direction were already in the single line section. The single line sections needed to be straight, so the profile of the line tended to be a series of chords
Chord (geometry)
A chord of a circle is a geometric line segment whose endpoints both lie on the circumference of the circle.A secant or a secant line is the line extension of a chord. More generally, a chord is a line segment joining two points on any curve, such as but not limited to an ellipse...
rather than a smooth arc
Arc (geometry)
In geometry, an arc is a closed segment of a differentiable curve in the two-dimensional plane; for example, a circular arc is a segment of the circumference of a circle...
.
Doubling and singling
When a single track railway is converted to a double track railway, in some countries this is called duplication or doubling. Converting a double track railway to a single track is known as singling. A double track operating only a single track is known as single-line workingSingle-line working
On a double track railway, single-line working refers to the practice of using one track out of two, usually when one of the tracks is out of use for maintenance or because of damage or some obstruction.- Circumstances :...
.