The Mainline or Main line of a railway is a track that is used for through trains or is the principal artery of the system from which branch lines, yards, sidings and spurs are connected.
It generally refers to a route between towns, as opposed to a route providing suburban or metro services. For capacity reasons, main lines in many countries will at a minimum be double tracked, and will often contain multiple parallel tracks.
Mainline tracks are typically operated at higher speeds than branch lines, and are generally built and maintained to a higher standard than yards and branch lines.
Railroad switches (points in the UK) are usually set in the direction of the main line by default. Failure to do so has been a factor in several fatal railway accidents, for example the Buttevant Rail Disaster in Ireland,[1] and the Graniteville train disaster in the US.[2]
Mainlines may also be operated under shared access by a number of railway companies, with sidings and branches operated by private companies or single railway companies.
In the UK, the term "Mainline" may also be used to distinguish any train or track that is not part of a light-rail or Underground network.