London Underground with smaller trains that run in two circular tunnels ("tubes") with a diameter about . These lines have the exclusive use of a pair of tracks, except for the Piccadilly line, which shares track with the District line between Acton Town and Hanger Lane Junction and with the Metropolitan line between Rayners Lane and Uxbridge; and the Bakerloo line, which shares track with London Overground services north of Queen's Park. Fifty-five per cent of the system runs on the surface. There are of cut-and-cover tunnel and of tube tunnel. Many of the central London underground stations on deep-level tube routes
West London Orbital the Mayor's Transport Strategy was published, which includes a proposal for this 'orbital' connection to Old Oak between Hounslow and Brent Cross. The London Mayor's Transport Strategy (MTS), published on 28 February 2018 and ratified by the London Assembly on 8 March 2018, includes plans for a West London Orbital railway line under Proposal 88. The mayor’s proposal for the service highlights that utilising new and existing orbital connections in west London could also improve public transport connections in the city centre. It reads: “Most Londoners want to move around London – rather than in and out of the centre