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| ELR | Route | Section | Remarks |
|---|---|---|---|
| TAD | Trecwn Branch | Letterston Jn to Trecwn | |
| TAH1 | Tottenham and Hampstead Line | Junction Road Jn to South Tottenham East Jn | |
| TAH2 | Tottenham and Hampstead Line | South Tottenham East Jn to Woodgrange Park Jn | |
| TAH3 | Tottenham and Hampstead Line | Woodgrange Park Jn to Barking Tilbury Line Jn | |
| TAH4 | Tottenham and Hampstead Line | Barking Station Jn to Barking (Platform 1) | |
| TAT | Tattenham Corner (or Tadworth or Chipstead) Branch | Purley Jn to Tattenham Corner | |
| TBD | Taff Bargoed Branch | Taff Bargoed Branch Jn to Cwmbargoed | |
| TBH1 | Three Bridges Jn to Havant Jn | Three Bridges Jn to Arundel Jn (North) | |
| TBH2 | Three Bridges Jn to Havant Jn | Arundel Jn (South) to Havant Jn | |
| TCC | Erewash Valley Line | Trent East Jn to Clay Cross South Jn | |
| TCW1 | Temple Hirst Jn to Selby South Jn | ||
| TEN | Stansted East to North Loop | Stansted North Jn to Stansted East Jn | |
| TES | Sheet Stores Curve | Trent East Jn to Sheet Stores Jn | |
| TEY | Tyne Yard | ||
| TFC | Thornton’s Field Sidings | Understood to be disused | |
| TFN | Trimley Jn to Felixstowe Port (NR boundary) | ||
| THA | Thame Branch | Kennington Jn to Cowley | Understood to be mostly closed between Thames Jn (~0M 1320y) and Cowley Works (~15M 0660y) |
| THG | Thorpe Goods Sidings | ||
| THL | Trent South Jn to Toton Jn (High Level Goods Line) | ||
| THN | Thames Haven Branch | Thames Haven Jn to Thames Haven | |
| THO | Thornbury Branch | Yate Middle Jn to Tytherington | |
| THT | Treherbert Branch | Pontypridd North Jn to Treherbert | |
| TIR | Tilbury Riverside Branch | Tilbury West Jn to Tilbury Riverside | Understood to be mostly disused |
| TJC1 | Tapton Jn (Chesterfield) to Colne | Tapton Jn to Freight Terminal Jn | |
| TJC2 | Tapton Jn (Chesterfield) to Colne | Freight Terminal Jn to ELR change | |
| TJC3 | Tapton Jn (Chesterfield) to Colne | former Masborough Station South Jn to former Skipton North Jn | Understood to be disused 166M 1320y to 175M 1715y and 181M 1650y to 184M 1235y |
| TJG1 | Thorne Jn to Gilberdyke | Thorne Jn to Thorne North | |
| TJG2 | Thorne Jn to Gilberdyke | Thorne North to Gilberdyke | |
| TJY | Tavistock Jn Marshalling Yard | ||
| TLA | Stansted Airport Branch | Stansted South Jn to Stansted Airport | |
| TLL | Tilbury Loop Line | Barking Tilbury Line East Jn to Pitsea Jn | |
| TLP1 | Tonbridge Loops | Bickley Jn to Petts Wood Jn | |
| TLP2 | Tonbridge Slow Loops | Bickley Jn to Petts Wood Jn | |
| TMD1 | Temple Mills Depot Branch | Stratford International West Jn to Temple Mills Depot | |
| TML | Channel Tunnel Connection Jn to Maintenance Boundary with Eurotunnel | TML: Trans-Manche Link | |
| TMP | Thorpe Marsh Power Station Branch | Thorpe Marsh Power Station Branch | Understood to be disused |
| TNC | Treeton North Curve | Treeton North Jn to Catcliffe Jn | Understood to be disused |
| TNW | Thornton West Curve | Thornton West Jn to Thornton North Jn | |
| TOR | Torquay Branch | Newton Abbot West Jn to Goodrington (via Torquay and Paignton) | |
| TPS1 | Trafford Park Jn to Manchester Ship Canal (MSC) Sidings | ||
| TPS2 | Bridgewater Jn to Metropolitan Vickers Sidings | ||
| TPS3 | Trafford Park Jn to Trafford Park West Jn | ||
| TRL1 | Channel Tunnel Rail Link (CTRL / HS1) | London St Pancras International to York Way South Jn | |
| TRL2 | Channel Tunnel Rail Link (CTRL / HS1) | York Way South Jn to Dagenham Jn | |
| TRL3 | Channel Tunnel Rail Link (CTRL / HS1) | Dagenham Jn to Folkestone Eurotunnel Terminal (CTRL / ET boundary) | |
| TRL5 | Channel Tunnel Rail Link (CTRL / HS1) | North Kent Line Connection Jn to Springhead Jn | |
| TRL6 | Channel Tunnel Rail Link (CTRL / HS1) | Ashford West Jn to Ashford International | CTRL Ashford Chord Line |
| TRL7 | Channel Tunnel Rail Link (CTRL / HS1) | Ashford International to Ashford East Jn | CTRL Ashford Chord Line |
| TRL8 | Channel Tunnel Rail Link (CTRL / HS1) | Dollands Moor West Jn to Dollands Moor Yard Freight Chord | |
| TSB | Birmingham and North Warwickshire Line | Tyseley South Jn to Bearley Jn | |
| TSC | Tibshelf & Blackwell Branch Jn to Silverhill Colliery and Extension | Understood to be disused | |
| TSE1 | South Tottenham East Jn to Tottenham West Jn | ||
| TSE2 | Tottenham South Curve | Tottenham South Jn to Tottenham West Jn | |
| TSJ | Kingston Loop | Twickenham Jn to Shacklegate Jn | |
| TSN1 | Trent South Jn to Nottingham | Trent South Jn to Mansfield Jn | |
| TSN2 | Trent South to Nottingham | Nottingham East Jn to Mansfield Jn | |
| TSO | Thurso Branch (Far North Line) | Georgemas Jn to Thurso | |
| TSS | Muirhouse Central Jn to Terminus Jn | ||
| TST | Sheffield Tram Transfer Line | ||
| TSY | Tees Yard Sidings | ||
| TTA1 | Chinley to Ashburys Line | Chinley North Jn to former Reddish Jn | |
| TTA2 | Chinley to Ashburys Line | former Reddish Jn to Ashburys East Jn | |
| TTE | Tilbury Marine Spur | Tilbury Riverside to Tilbury East Jn | Understood to be mostly disused |
| TTF | Totton, Hythe, and Fawley Light Railway | Totton East Jn to Fawley | |
| TTH | Tonbridge to Hastings Line | Tonbridge East Jn to Hastings | |
| TUR | Turnchapel Branch | Turnchapel Branch Jn to Plymstock | Understood to be part closed |
| TWN | Thorpe-le-Soken to Walton-on-the-Naze | ||
| TYB1 | Torksey Branch | Clarborough Jn - Cottam Power Station | |
| TYC | Thoresby Colliery Branch | Thoresby Colliery Jn to Thoresby Colliery |