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
M25 motorway began in 1973. The first section, between South Mimms and Potters Bar in Hertfordshire (junction 23 to junction 24) opened in September 1975 and was given the temporary general purpose road designation A1178 (a section of motorway-standard-road, originally the M16, which eventually was incorporated into the M25) was completed and operational before this. A Watford-avoiding route between the M1 and the A40 between north Watford and Denham was locally known as the Croxley Green/Rickmansworth bypass, and was operational about 1973/4; a section south of London (junction 6 to junction 8) opened in 1976. A section of Ringway 3 south of