A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
| ELR | Route | Section |
|---|---|---|
| AAV | Ascot and Ash Vale Line | Ascot to Ash Vale Jn |
| ABD | Aberdare Branch | Abercynon Jn to former Cwmbach New Jn |
| ABE1 | Allington West Jn to former Barkston East Jn | |
| ABW | Abbotswood Branch | Abbotswood Jn to Norton Jn |
| ACD | Allington Chord | Allington East Jn to Allington North Jn |
| ACP ℹ️ | Avenue Coke Plant | Clay Cross North Jn to Avenue Coke Plant |
| ACR | Ashford E Jn to Ramsgate (via Canterbury West) | |
| ACW | Acton Branch | Acton Canal Wharf Jn to Willesden Jn |
| AEG | Allerton Curve | Allerton East Jn to Garston Jn |
| AFE | Shrewsbury Loop | Abbey Foregate Jn to English Bridge Jn |
| AFL | Aintree Fork Line | former Sefton Jn to Aintree Emergency GF |
| AFR | Avonmouth and Filton Line | Stoke Gifford Jn No.2 to Bristol Bulk Handling Terminal |
| AFS ℹ️ | Aviemore to Forres | |
| AGW | Angerstein Wharf Branch | Angerstein Jn to Angerstein Wharf |
| AGY | former Grimesthorpe Jn to Attercliffe Goods Yard | |
| AHB ℹ️ | Ashburton Branch | Ashburton Jn to Ranney LX |
| AHG | Waterloo Curve | Nine Elms Jn to Linford Street Jn |
| AHX | Hunts Cross Chord | Allerton Jn to Hunts Cross West Jn |
| AIW ℹ️ | Alton Itchen Abbas and Winchester Line | Alton: NR to Mid-Hants Railway interface |
| AJB | Addlestone Jn to Byfleet Jn | |
| AJM1 ℹ️ | Matlock Branch | Ambergate Jn to Matlock Riverside |
| ALC1 | Aston and Lichfield Cross City Line (North) | Aston North Jn to Sutton Coldfield |
| ALC2 | Aston and Lichfield Cross City Line (North) | Sutton Coldfield to Lichfield City Jn |
| ALK | Aberdare Link Line | former Cwmbach New Jn to former Cwmbach Jn |
| ALN1 ℹ️ | Haltwhistle to Alston | Haltwhistle Sidings |
| AMB ℹ️ | Avonmouth Branch | Severn Beach to St Andrews Jn |
| AMJ | Ashton Moss Curve | former Ashton Moss South Jn to Ashton Moss North Jn |
| AML | Attenborough Jn to Meadow Lane Jn | |
| ANI1 ℹ️ | Aberdeen to Inverness Line | Aberdeen to Keith Jn |
| ANI2 ℹ️ | Aberdeen to Inverness Line | Keith Jn to Forres |
| ANI3 ℹ️ | Aberdeen to Inverness Line | Forres (excl.) to Milburn Jn |
| ANL ℹ️ | Acton and Northolt Line | former Old Oak Common West Jn to Northolt Jn |
| ANN | Ayr and Mauchline Line | Newton Jn to Mauchline Jn (via Annbank Jn) |
| ANS | Aldwarke Jn to Aldwarke Jn South | |
| APG ℹ️ | Aberpergwm Branch | former Aberpergwm Branch Jn to Glyn Neath Works Sidings |
| APL | Dungeness Branch | Appledore Jn to Lydd Town |
| APS | Aberthaw Power Station Branch | |
| APY ℹ️ | Austin Pickersgills Yard | former Monkwearmouth Jn to Yard |
| AQL | Arcow Quarry Line | Arcow Quarry GF to Arcow Quarry |
| ARG1 ℹ️ | Argyle Line | Rutherglen Central Jn to former Strathclyde Jn |
| ARG2 ℹ️ | Argyle Line | former Strathclyde Jn to Finnieston East / West Jns |
| ARH | Ardrossan Harbour Branch | Holm Jn to Ardrossan Harbour |
| AST ℹ️ | Astley Bridge (or Halliwell) Branch | former Astley Bridge Jn to Astley Bridge |
| ATG | NR / TfL boundary (Turnham Green) to Gunnersbury Jn | |
| ATH | Ashford D Jn to Hastings | |
| ATL | Atlantic (or South London) Line | Peckham Rye Jn to Battersea Park Jn |
| AWL | Acton Wells Branch | Acton East Jn to Acton Wells Jn |
| AWP | Cottingham Branch | Anlaby Road Jn to West Parade North Jn |
| AYH1 | Ayr Harbour Branch | Newton Jn to Ayr Harbour (NR boundary) |
| AYH2 | Ayr Harbour Branch | Falkland Jn to Ayr Harbour Jn (via Falkland Yard) |
| AYR1 | Glasgow to Ayr | Bridge Street Jn to Paisley Gilmour Street |
| AYR2 ℹ️ | Glasgow to Ayr | Paisley Gilmour Street |
| AYR3 ℹ️ | Glasgow to Ayr | Paisley Gilmour St (excl.) to former Dalry Jn |
| AYR4 | Glasgow to Ayr | former Dalry Jn to Barassie Jn |
| AYR5 | Glasgow to Ayr | Barassie Jn to former Lochgreen Jn |
| AYR6 | Glasgow to Ayr | former Lochgreen Jn to Ayr |
| AYS | Ashburys Yard Sidings |