Thorney Interchange
The Thorney Interchange is a large motorway intersection in the UK, between the M4 and M25. It is one of the busiest motorway interchanges in the UK. It is situated directly on the edge of Buckinghamshire, Greater London (London Borough of Hillingdon) and Berkshire. It is also not too far from Surrey and Staines-upon-Thames. History The M4 (London-South Wales Motorway) under the interchange was opened in December 1964, from junctions 4 (A408) to 5; this 3.9-mile section cost £3.2m, and was built by Cubitts and Green. The interchange, hence, is junction 4b of the M4. The interchange is around one mile north-west of Heathrow Airport; the interchange is the main junction for traffic heading from the M25 to the airport. The interchange is the point that the M4 enters Greater London. Design The bridge decks were to be built of prestressed concrete, but instead were built with composite steel beams and concrete decks, designed to BS 5400. In the early 1980s, when the interchange was being built, the entire M25 was to cost around £600m. The southern part of the M4/M25 interchange was part of a 2.05-mile section of the M25 which was due to open in spring 1985, the