Engineer's Line Reference
An Engineer's Line Reference (or ELR for short) is a three or four-character code used in the British rail network to refer to a section of a track or route. These references are unique across the whole rail network, allowing identification of any part of the network. Occasionally ELRs are used to refer to other railway infrastructure such as depots.
ELRs are usually made up of three letters, identifying the route. Any place on that route can then be referred to by using a combination of the ELR and the mileage of the place, e.g. EJM 13m 16c refers to Plessey Road Level Crossing on the Earsdon Junction (EJ) to Morpeth North Junction (M). The crossing is 13 miles and 16 chains from the origin point of 0miles 0 chains.
Where a route is long or made up of a combination of several pre-existing routes, the ELR is suffixed with a number that refers to a particular section of the route - e.g. the East Coast Main Line route (with a reference of ECM) has sections ECM1 (King's Cross to Shaftholme Junction) through to ECM9 (Edinburgh Waverley Station.)
ELRs are generally abbreviated forms of the names of the primary locations they connect. For example XTD is the line which runs from Charing Cross to Dover or VTB for the line from Victoria to Brighton. Sometimes the ELRs are less obvious - NKL, for example, runs from North Kent East junction to Dartford junction but is known as the North Kent line, hence its ELR.
ELRs differ from LORs (lines of route), not only in their use and format, but also in what they demarcate. Lines of route refer to strategic rail routes, and can be made up of several ELRs. For example, SBJ is the ELR for the line between Swanley and Ashford B junction. At Otford junction, the line diverges to Sevenoaks with an ELR of OJS. The line of route which covers Swanley to Sevenoaks is SO140. The LOR reference for any UK location can be found in the page heading of the Sectional Appendix line diagrams.
An authoritative reference to ELRs is available on Phil Deaves' Engineers' Line References page.