Thorney Interchange
| Thorney Interchange | |||
| Location Map ( geo) | |||
 | |||
| |||
| Location | |||
| Colnbrook | |||
| County | |||
| Buckinghamshire • Middlesex | |||
| Highway Authority | |||
| National Highways | |||
| Junction Type | |||
| 4-level stack | |||
| Roads Joined | |||
| M4, M25 | |||
Thorney Interchange, also known as Colnbrook Interchange is the junction between the M4 and M25. It is one of three four level stack interchanges in the country. For the M4, it is junction 4B, whilst it is junction 15 for the M25.
History
The M4 Motorway was opened here in March 1965. The M25 was constructed in the 1980s, with the section through the interchange opening to traffic on 18 September 1985. The connecting roads were only partially completed, just allowing M25N to M4W and M4E to M25N. The interchange was fully completed and opened on 19 December 1985.
In order to construct the interchange the main carriageways of the M4 were diverted either side of the central core of the interchange in order to allow construction of the bridge carrying the M4 over the M25 to M4 slip roads, as well as the bridge carrying the M25 over the M4, and the high level bridges carrying M4 to M25 traffic. In addition, the whole interchange also bridges over a railway line.
As part of the interchange construction, the M4 was widened to the east to Junction 4.
Routes
| Route | To | Notes |
| The WEST, Slough, Reading | ||
| London (W & C), Heathrow Airport (Terminals 1, 2 & 3), Central London, Hammersmith | ||
| (M40, M1, M11), Oxford, Watford, Stansted Airport | ||
| Heathrow Airport (Terminals 4, 5 & Cargo), (M3, M23, M20), Gatwick Airport, Dartford |
