Engineers line reference

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Engineers' line reference (ELR) is a four-character code used in the British railway network (Network Rail and its train operating customers) as designations for portions of track. These references are unique to each section and enable greater specificity, aiding the management of the operational railway.

The code is alphanumeric with three letters followed by a number, usually zero, but in areas where the line is straightforward but particularly long, it is split up into sections, marked out by a change in the number. This also occurs in areas where complex junctions occur or where antiquated line names remain. Increasingly, however, the zero is dropped where the line is not split (i.e. end-to-end), leaving three letters only - the number only being introduced where splits occur (e.g. ECM1 for East Coast Mainline part 1, ECM2 for East Coast Mainline part 2, etc.).

The ELRs formation are generally named as an acronym of the primary locations they connect. For example XTD0 is the line which runs from Charing Cross to Dover via Tonbridge. Sometimes, however the ELRs are less obvious, NKL0, for example runs from North Kent East junction to Dartford junction, but is simply 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. For example, SBJ0 is the ELR for the line between Swanley and Ashford B junction. This line diverges at Otford junction to another line, which then links Otford junction to Sevenoaks. This second line has its own ELR (OJS0 - Otford junction to Sevenoaks), however SO140 is the LOR for Swanley to Ashford and to Sevenoaks, thus including SBJ0 and OJS0.