|The four-levels, viewed from the M25|
|Modified Directional-T/Modified 4-level Stack|
Chiswell Interchange is a major junction between the M1 and M25 motorways near St Albans in Hertfordshire, and was opened in October 1986 as part of the last section of the M25. For the M1, it is junction 6a, whilst it is junction 21 for the M25. The junction is a modified directional-T style interchange, with the modification being that instead of terminating, the M1 continues through the junction. No links from or to the southern M1 are provided.
In other words it is a four-level stack with the south-facing slip roads omitted.
It has the additional complication that its eastern slip roads are interlaced with the western slips of M25 J21A.
|The NORTH, Luton Airport|
|London, Watford||access/exit from/to M25 via nearby A405|
|Stansted Airport (M11), Dartford Tnl (M20), Stevenage (A1(M))||as signed on M25|
|(M11, M20), Stansted Airport, Dartford||as signed down sliproad from M1|
|Heathrow Airport M4, Aylesbury A41||as signed on M25|
|(M40, M4, M3) Heathrow Airport||as signed down sliproad from M1|
|St Albans, London (N.W.), (M1 South)||west facing M25 slips of junction 21a braided into the junction|