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| ELR | Route | Section | Remarks |
|---|---|---|---|
| SAA | Stirling to Dunfermline | Stirling Middle Jn to former Kincardine Jn | SAA: Stirling to Alloa |
| SAC | Settle and Carlisle Line | Settle Jn to Petteril Bridge Jn | |
| SAG | St Andrew’s Curve | St Andrew’s Jn to Grand Jn | |
| SAJ | Stalybridge Branch | Guide Bridge West Jn to Stalybridge Jn | |
| SAL | Salisbury Branch | Westbury South Jn to Wilton Jn | |
| SAN | Santon Iron Ore Branch | Foreign Ore Branch Jn to Scunthorpe Steelworks | |
| SAR1 | North London Line | South Acton Jn to Gunnersbury Jn | |
| SAR2 | North London Line | Gunnersbury Jn to Richmond | |
| SAS | Stechford and Aston Line | Stechford South Jn to Aston South Jn | |
| SAW | Severn and Wye Line | Berkley Road Jn to Sharpness New Dock (NR boundary) | |
| SBA1 | Shrewsbury and Welshpool Line | Sutton Bridge Jn to former Buttington Jn | |
| SBA2 | Shrewsbury and Welshpool Line | former Buttington Jn to Aberystwyth | |
| SBF | Shipley East Jn to Bradford Forster Square | ||
| SBH1 | Springs Branch Jn (Wigan) to Huyton | Huyton Jn to St Helens Station Jn | |
| SBH2 | Springs Branch Jn (Wigan) to Huyton | St Helens Station Jn to Gerard’s Bridge Jn | |
| SBH3 | Springs Branch Jn (Wigan) to Huyton | Gerard’s Bridge Jn to Springs Branch Jn | |
| SBJ | Swanley Jn to Ashford ‘B’ Jn (via Charing) | ||
| SBK1 | Sudbrook Branch | Caldicot to COM | Understood to be disused |
| SBK2 | Sudbrook Branch | COM to Sudbrook | Understood to be disused |
| SBO | Borders Railway | Newcraighall South Jn to Tweedbank | |
| SBR | Shepreth Branch | Hitchin to Shepreth Branch Jn | |
| SCB | Skegby (or Brierley) Branch | Sutton Colliery Jn to Sutton Colliery | Understood to be disused |
| SCC | Sheepcote Curve | West London Jn to Latchmere No. 3 Jn | |
| SCD | Scunthorpe Trent Jn to Dawes Lane Jn | ||
| SCG | South Carlisle Goods Line | Carlisle Bog Jn to Forks Jn | |
| SCL | Soho Curve | Soho East Jn to Soho North Jn | |
| SCM1 | Scottish Central Main Line | Motherwell Jn to Mossend South Jn | |
| SCM2 | Scottish Central Main Line | Mossend South Jn to Whifflet North Jn | |
| SCM3 | Scottish Central Main Line | Whifflet North Jn to Dunblane (former Oban Jn) | |
| SCM4 | Scottish Central Main Line | Dunblane (former Oban Jn) to Perth South Jn | |
| SCM5 | Scottish Central Main Line | Dundee Central Jn to Perth South Jn | |
| SCN | Ship Canal Branch | Eccles Station Jn to Weaste | |
| SCP | Sydenham Jn to Crystal Palace Tunnel Jn | ||
| SCQ1 | Stoke to Caldon Quarry | Stoke Jn to Milton Jn to Congleton | Understood to be part closed |
| SCQ2 | Stoke to Caldon Quarry | Milton Jn to Leek Brook Jn | Understood to be disused |
| SCQ3 | Stoke to Caldon Quarry | Leek Brook Jn to Caldon Quarry | Understood to be part closed |
| SCR | Speke and Garston Line | Speke Jn to Garston Docks | Known anomalies with data source accuracy |
| SCT1 | Bootle Branch | Bootle Branch Jn to Canada Dock Goods | Understood to be part closed |
| SCT2 | Bootle Branch | Atlantic Dock Jn to Alexandra Dock Goods (NR boundary) | |
| SCU1 | South Croydon Jn to Uckfield | ||
| SDC | Stratford Central Jn to Coppermill North Jn | ||
| SDG | Snodgrass Branch | Bogside Junction to ICI Snodgrass (NR boundary) | Understood to be disused |
| SDI1 | Swansea District Line | Briton Ferry to Jersey Marine Jn (Up Flying Loop) | |
| SDI2 | Swansea District Line | Jersey Marine Jn to Morlais Jn | |
| SDJ2 | Skelton Jn to Ditton Jn | Understood to be part closed | |
| SDP | Swindon Locomotive Depot and Stores Sidings | ELR SDP is not geographically related to SDP1 or SDP2 | |
| SDP1 | St Denys to Portcreek | St Denys Jn to Fareham East Jn | ELRs SDP1 and SDP2 are not geographically related to SDP |
| SDP2 | St Denys to Portcreek | Fareham East Jn to Portcreek Jn | ELRs SDP1 and SDP2 are not geographically related to SDP |
| SDS | St Dennis Branch | Burngullow Jn to Parkandillack | |
| SEA1 | Seafields Branch | Dawdon Jn to Seaham Harbour NR boundary | |
| SEC | Selby Canal Goods Line | Selby Canal Jn to Selby West Jn | |
| SEJ1 | Sittingbourne Eastern Jn to Sheerness-on-Sea | Sittingbourne Eastern Jn to Sittingbourne Middle Jn | |
| SEJ2 | Sittingbourne Eastern Jn to Sheerness-on-Sea | Sittingbourne Middle Jn to Sheerness-on-Sea | |
| SEL | Tinsley South Jn to Shepcote Lane West Jn | ||
| SEN | Syston North Curve | Syston East Jn to Syston North Jn | |
| SES | Seal Sands Branch | Seal Sands Branch Jn to Seal Sands Simon Storage | |
| SEV | Sevington Freight Yard | ||
| SEY | Seymour Colliery Branch | Seymore Jn to Seymore Colliery | Understood to be disused |
| SFO | Todmorden Curve (or Stansfield Hall Fork) | Todmorden Viaduct Jn to Stansfield Hall Jn | |
| SFQ | Stud Farm Quarry Branch | Bagworth Jn to Stud Farm Quarry | |
| SGN | Springburn Branch | Cowlairs West Jn to Bellgrove Jn | |
| SHB | Sheffield and Barnsley Line | Wincobank Jn to former Quarry Jn | |
| SHF | Strawberry Hill Jn to Fulwell Jn | ||
| SHG | Sherburn Curve | Sherburn Jn to Gascoigne Wood Jn | |
| SHL | Shrewsbury and Hereford Line | Shrewsbury Severn Bridge Jn to former Rotherwas Jn | |
| SHR | Wishaw Connecting Line | Wishaw Central Jn to Shieldmuir North Jn | |
| SHS1 | St Helens Line | Sutton Oak Jn to St Helens Station Jn | Understood to be disused |
| SHW | Robin Hood Line | Shireoaks West Jn to Woodend Jn | |
| SIB1 | Chesterton Jn to Fen Drayton | Understood to be disused | |
| SIC1 | Silverwood Colliery Branch | Headshunt to 11 MP | Understood to be disused |
| SIC2 | Silverwood Colliery Branch | 11 MP to Thrybergh Jn | Understood to be disused |
| SIL | Stock Interchange Line | Paradise Jn to Derby Square Jn | |
| SIV | St Ives Branch | St Erth to St Ives | |
| SIZ | Saxmundham Jn to Leiston | Sizewell Sidings | |
| SJB | St James Jn to Bridge Jn | ||
| SJC | former Carnforth East Jn to former Wennington Jn | ||
| SJD | Skelton Branch | Skelton Jn to Deansgate Jn | |
| SJM1 | Swinton to Mexborough | Swinton South Jn to Swinton Jn | |
| SJM2 | Swinton Curve | Swinton Jn to Mexborough West Jn | |
| SJO1 | Mersey Northern Line | Walton Jn to Sandhills Jn | |
| SJO2 | Mersey Northern Line | Walton Jn to Ormskirk | |
| SJS | Stourbridge Town Branch | Stourbridge Jn to Stourbridge Town | |
| SJT1 | Blisworth, Stratford-upon-Avon, and Broom Line | Understood to be part closed | |
| SKA | Skellow Jn to Adwick Jn | ||
| SKD | Swansea King’s Dock Line | Burrows Jn (King’s Dock) to South Dock Jn | |
| SKL | Stocksbridge Light Railway | ||
| SKM | South Kirkby Curve (or Moorthorpe Loop) | South Kirkby Jn to Moorthorpe Station Jn | |
| SKN | Birmingham and Gloucester Line | St Andrew’s Jn to Kings Norton | |
| SKS1 | Skipton to Swinden | Skipton Station North Jn to Embsay Jn | |
| SKS2 | Skipton to Swinden | Embsay Jn to Grassington | Understood to be part closed |
| SKW1 | Skipton to Wennington Jn | ||
| SLC1 | Stewarts Lane Depot | Non-Electrified Roads 1-4 | Road 1 adjacent to Road 22 (on ELR SLC8) |
| SLC8 | Stewarts Lane Depot | Carriage Depot (Electrified Roads 1-22) | Road 22 adjacent to Road 1 (on ELR SLC1) |
| SLJ | Streatham Local Spur | Streatham North Jn to Streatham South Jn | |
| SLT | Stonebridge Park to LTE Depot | ||
| SMA | South Manchester Airport Chord | Heald Green West Jn to Heald Green South Jn | |
| SMJ1 | Swinton Jn to Milford Jn Line | Swinton Jn to former Dearne Jn | |
| SMJ2 | Swinton Jn to Milford Jn Line | former Dearne Jn to Burton Salmon Jn | |
| SMJ3 | Swinton Jn to Milford Jn Line | Burton Salmon Jn to Milford Jn | |
| SMS1 | Streatham to Sutton, via Wimbledon and Morden | Streatham South Jn to Wimbledon ‘A’ Jn | |
| SMS2 | Streatham to Sutton, via Wimbledon and Morden | Wimbledon ‘A’ Jn to Sutton Wimbledon Line Jn | |
| SNJ | Middlewich Branch | Sandbach North Jn to Northwich West Jn | |
| SNK1 | King’s Dock Branch | Swansea Docks King’s Dock Jn to ‘D’ Shed | Understood to be part closed |
| SNS | Streatham Main Spur | Streatham North Main Line Jn to Streatham South Main Line Jn | |
| SNT | Swindon Transfer Yard | ||
| SNW | Sleaford North Jn to Sleaford West Jn | ||
| SOB1 | Soham Branch | Chippenham Jn to former Snailwell Jn | |
| SOB2 | Soham Branch | former Snailwell Jn to Ely Dock Jn | |
| SOL | South Lynn Branch | Understood to be disused | |
| SOT | Seaton Snook Goods Branch | Seaton Snook Jn to Seaton-on-Tees | |
| SOY | Northam Jn to Southampton Eastern Docks | ||
| SPC1 | London St Pancras to Chesterfield – Midland Main Line (MML) | London St Pancras to Bedford | |
| SPC2 | London St Pancras to Chesterfield – Midland Main Line (MML) | Bedford to Wellingborough | |
| SPC3 | London St Pancras to Chesterfield – Midland Main Line (MML) | Wellingborough to Wigston South Jn | |
| SPC4 | London St Pancras to Chesterfield – Midland Main Line (MML) | Wigston South Jn to Leicester | |
| SPC5 | London St Pancras to Chesterfield – Midland Main Line (MML) | Leicester to Ratcliffe Jn | |
| SPC6 | London St Pancras to Chesterfield – Midland Main Line (MML) | Ratcliffe Jn to Derby Jn | |
| SPC7 | London St Pancras to Chesterfield – Midland Main Line (MML) | Spondon to Derby London Road Jn | Spondon Curve |
| SPC8 | London St Pancras to Chesterfield – Midland Main Line (MML) | Derby London Road Jn to Clay Cross South Jn | |
| SPC9 | London St Pancras to Chesterfield – Midland Main Line (MML) | Clay Cross South Jn to Tapton Jn | |
| SPD1 | Spalding and Doncaster Line | Spalding South Jn to Sleaford South Jn | |
| SPD2 | Spalding and Doncaster Line | Sleaford South Jn to Greetwell West Jn | |
| SPD3 | Spalding and Doncaster Line | Greetwell West Jn to Trent East Jn | |
| SPD4 | Spalding and Doncaster Line | Trent West Jn to Bessacarr | |
| SPD5 | Spalding and Doncaster Line | Bessacarr to Decoy North Jn Doncaster | |
| SPW | Springbank Road Jn to Walton Street Jn | ||
| SRD | St Helens to Rainford | Gerard’s Bridge Jn to Rainford Jn | Understood to be part closed |
| SSC | Streatham Spur | Streatham Jn to Streatham Common Jn | |
| SSE | Sleaford South Jn to Sleaford East Jn | ||
| SSJ1 | Sheet Stores Jn to Chellaston East Jn | ||
| SSJ2 | Chellaston West Jn to Stenson Jn | ||
| SSK1 | Saltburn West Jn to Skinningrove (Cleveland Potash) | ||
| SSL | Seven Sisters Chord / Loop | Seven Sisters Jn to South Tottenham West Jn | |
| SSP | Soho and Perry Barr Line | Perry Barr South Jn to Soho South | |
| SSS | Sharpness Dock South Branch | Sharpness South Jn to Sharpness Docks | |
| SSV | Shenfield Jn to Southend Victoria | ||
| STA | Staines Branch | West Drayton to Colnbrook | |
| STB | St Botolph’s Branch | East Gate Jn to Colchester Town | |
| STD | Stratford Branch | Honeybourne to Long Marston | |
| STF | Norton South Jn to Ferryhill South Jn | STF: Stillington to Ferryhill | |
| STM | Temple Mills Yard | Arrival and Departure Lines | |
| STN | Stranraer Harbour Jn to Stranraer Town | Understood to be disused | |
| STO | Stoke Works Branch | Droitwich Spa Jn to Stoke Works Jn | |
| STR1 | Stranraer Harbour Branch | Ayr to Girvan | |
| STR2 | Stranraer Harbour Branch | Girvan to former Challoch Jn | |
| STR3 | Stranraer Harbour Branch | former Challoch Jn to Stranraer Harbour Jn (or Yard) | |
| STR4 | Stranraer Harbour Branch | Stranraer Harbour Jn (or Yard) to Stranraer | |
| STS | Seaford Branch | Southerham Jn to Seaford | |
| STY | Styal Line | Wilmslow Jn to Slade Lane Jn | |
| SUB1 | Edinburgh South Suburban (Sub) Line | Portobello Jn to former Niddrie North Jn | former Niddrie North Jn also known as former Lothian Lines Jn |
| SUB2 | Edinburgh South Suburban (Sub) Line | Haymarket Central Jn to former Niddrie North Jn | former Niddrie North Jn also known as former Lothian Lines Jn |
| SUD | Sudbury Branch | Marks Tey Jn to Sudbury | |
| SUT1 | Sutton Harbour Branch (Plymouth) | Laira Jn to Mount Gold Jn | |
| SUT2 | Sutton Harbour Branch (Plymouth) | Mount Gold Jn to former Friary Jn | |
| SWA | Swansea High Street Branch | Landore Jn to Swansea | |
| SWB | South Wales and Bristol Direct Line | Wootton Bassett Jn to Patchway No. 2 Jn | |
| SWE | Windsor Branch | Staines Jn to Windsor and Eton Riverside | |
| SWL | Swansea Loop | Swansea Loop East Jn to Swansea Loop West Jn | |
| SWM1 | South Wales Main Line (SWML) | Swindon Jn to Standish Jn | |
| SWM2 | South Wales Main Line (SWML) | Gloucester Yard Jn to Johnston | |
| SWP | Shirebrook Jn to Warsop Jn | ||
| SWX | Staines West Link Line (via former Staines West Jn) | Understood to be disused | |
| SWY | Stert and Westbury Line | former Patney & Westbury (or Chirton) Jn to Westbury North Jn | |
| SYC | Shrewsbury to Crewe Line | Shrewsbury Crewe Jn to Crewe South Jn | |
| SYE | (Coatbridge) Sunnyside Loop | Whifflet South Jn to Sunnyside Jn | |
| SZS | Willesden South West Sidings |