Single track (rail)

For other uses, see Single track.

Not to be confused with Monorail.

A train on the Kyle of Lochalsh Line, a single track railway in Scotland

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.

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 trains 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 loops (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 collisions 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 wagonways 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.

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 working.

New bike paths and railway corridors

Building bike trails on rail corridors is popular. Developing rail right of ways for a bike trail can restrict a train corridor to a single track. Also reclaiming a railway corridor to use trains again, that have become bike paths, limits the use of double tracks. The bike path is usually where the second track would be. An example of a bike, single track corridor is the E&N railroad in Victoria, Canada.

External links

• rails to trails