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 |
|---|---|---|
| ICS | Ilford Carriage Sidings | |
| IGE | Inverkeithing North Curve | Inverkeithing East Jn to Inverkeithing North Jn |
| ILK1 | Ilkley Branch | Apperley Jn to former Burley Jn |
| ILK2 | Ilkley Branch | former Burley Jn to Ilkley |
| IMG ℹ️ | Bamfurlong Sidings Curve | Bamfurlong Sidings Jn to Ince Moss Jn |
| INS | Inverness Harbour Branch | former Inverness Harbour Branch Jn to Inverness Harbour NR boundary |
| INW | Immingham West Jn to Immingham western storage | |
| IOW | Isle of Wight Railway | Ryde Pier Head to Shanklin |
| IPD ℹ️ | Ipswich Docks Branch | |
| ISC ℹ️ | Isabella Colliery Branch | former Newsham North Jn to Port of Blyth (Bates Staithes) |
| IUP ℹ️ | Ipswich Upper Yard |