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| ELR | Route | Section | Remarks |
|---|---|---|---|
| GAE | Gaer Branch | Gaer Jn to Park Jn | |
| GAW1 | Garw Valley Branch | Ogmore Jn to Caerdu Jn | |
| GAW2 | Garw Valley Branch | Caerdu Jn to Blaengarw | Understood to be disused |
| GBK | Glasgow, Barrhead, and Kilmarnock Railway | Muirhouse South Jn to Kilmarnock Jn | |
| GBN | Guide Bridge East Curve | Guide Bridge East Jn to Guide Bridge North Jn | |
| GBS1 | Guide Bridge Sidings | Brookside Sidings | |
| GBS2 | Guide Bridge Sidings | Avenue Sidings | |
| GDL | Goole Dock Line | Mineral Jn to Goole Docks | Understood to be disused |
| GDW | Glossop Branch | Glossop to Dinting West Jn | |
| GEC | Greenford East Curve | Greenford South Jn to Greenford East Jn | |
| GES | GEC Siding to Stafford No. 4 | GEC: General Electric Company | |
| GFB | Gas Factory Jn to Bow Jn | ||
| GGE | Gorgie Loop | Gorgie Jn to Haymarket West Jn | |
| GGZ | Gwaun-Cae-Gurwen Loop | Understood to be disused | |
| GHE | Gartsherrie South Jn to Gartcosh Jn | ||
| GHL | Greenhill Connecting Line | Greenhill Upper Jn to Greenhill Lower Jn | |
| GHM | Goole High Level Mineral Line | Understood to be disused | |
| GIF1 | Giffen Branch | former Lugton Jn to former Barrmill Jn | Understood to be disused |
| GIF2 | Giffen Branch | former Barrmill Jn to former Giffen Jn | Understood to be disused |
| GIF3 | Giffen Branch | former Giffen Jn to former Kilbirnie Jn | Understood to be disused |
| GIF4 | Giffen Branch | former Kilbirnie Jn to Giffen | Understood to be disused |
| GIR | Girvan Jn to Girvan Freight Depot | Understood to be disused | |
| GJC | Gannow Jn to Colne | ||
| GJH | Longtown MOD Branch | Mossband Jn to MOD Longtown | Known anomalies with data source accuracy |
| GLA | Gaerwen to Amlwch | Understood to be disused | |
| GLT | Green Lane to Tyne Dock | ||
| GMC | Glazebrook to Godley | Woodley Jn to Bredbury Waste Disposal Siding | |
| GMH | Grangemouth Branch | Grangemouth Jn to Grangemouth NR boundary | |
| GMS | Grantham Sidings | ||
| GNE | Gunnie Yard to Sunnyside Jn | Understood to be disused | |
| GNN | Greenburn Opencast Line | Understood to be disused | |
| GNQ1 | Oswestry Branch | Gobowen to Oswestry Jn | |
| GNQ2 | Tanat Valley Branch | Llynclys Jn to Llanddu Jn | Understood to be disused |
| GNQ3 | Nantmawr Branch | Llanddu Jn to Nantmawr Quarry | Understood to be disused |
| GNQ4 | Whitchurch and Aberystwyth Line | Oswestry Jn to Llynclys Jn | Understood to be part closed |
| GNT | Garnant Branch | Pantyffynnon to former Gwaun-Cae-Gurwen Branch Jn | |
| GNY2 | Gloucester New Yard | ||
| GOB | Gulf Oil Refinery Branch | Gulf Oil Branch Jn to Waterston | |
| GOC | Goldthorpe Colliery Branch | Understood to be disused | |
| GOJ | Gospel Oak Jn to Junction Road Jn | ||
| GOU1 | Paisley Gilmour Street to Gourock | Wallneuk Jn to Paisley Gilmour Street (Stoneybrae) | |
| GOU2 | Paisley Gilmour Street to Gourock | Paisley Gilmour Street (Stoneybrae) to Gourock | |
| GRC1 | Grimethorpe Colliery | Dearne Valley North Jn to COM | Understood to be disused |
| GRC2 | Grimethorpe Colliery | COM to Grimethorpe | Understood to be disused |
| GRD | Greetland Jn to Dryclough Jn | ||
| GRE | Graham Road Curve | Reading Lane Jn to Navarino Road Jn | |
| GRS1 | Grantham to Skegness Line | Barkston South Jn to ELR change | |
| GRS2 | Grantham to Skegness Line | ELR change to Boston Sleaford Line Jn | |
| GRS3 | Grantham to Skegness Line | Boston Sleaford Line Jn to former Firsby East Jn | |
| GRS4 | Grantham to Skegness Line | former Firsby East Jn to Skegness | |
| GRW | Halifax Jn to Griffin Wharf | ||
| GSG | Salop Independent Lines | Gresty Lane No. 1 to Salop Goods Jn | |
| GSJ1 | Galton Jn to Stourbridge Jn | Galton Jn to Smethwick Jn | |
| GSJ2 | Galton Jn to Stourbridge Jn | Smethwick Jn to Stourbridge Jn | |
| GSM1 | Kettering North Jn to Melton Mowbray | Kettering North Jn to Manton Jn | |
| GSM2 | Kettering North Jn to Melton Mowbray | Manton Jn to Melton Jn | |
| GSM3 | Kettering North Jn to Melton Mowbray | Syston South Jn to Melton Jn | |
| GSM4 | Kettering North Jn to Melton Mowbray | Melton Jn to Nottingham | |
| GSM5 | Kettering North Jn to Melton Mowbray | Asfordby Business Park Spur (NR RIDC Melton) | RIDC: Rail Innovation and Development Centre |
| GSM6 | Kettering North Jn to Melton Mowbray | Asfordby Business Park Spur (North Chord) | |
| GSW | Glasgow and South Western Railway | Kilmarnock Jn to Gretna Jn | |
| GTW1 | Guildford North Jn to Wokingham Jn | Guildford North Jn to former Ash Jn | |
| GTW2 | Guildford North Jn to Wokingham Jn | former Ash Jn to Wokingham Jn | |
| GUD | Aberdeen South Jn to Guild Street NR boundary | Understood to be disused | |
| GUE2 | Guiseley to Shipley | Esholt Jn to Dockfield Jn | |
| GWA | Gwaun-Cae-Gurwen Branch | Gwaun-Cae-Gurwen Branch Jn to Gwaun-Cae-Gurwen | |
| GXO | Plumpton Jn to Glaxo Siding | Understood to be disused |