Four level stack interchangesThe M4 has two of the three four-level stack interchanges in the UK, including the first UK example at junction 20, the Almondsbury Interchange with the M5. The other is junction 4b with the M25.
J28 of the M1 is one of the most important logistics locations in the East Midlands. It is almost equidistant between Birmingham and Manchester, the UK's second and third largest cities. The junction is where the A38 links the M1 to Sutton and Mansfield and to Birmingham via Derby.
By October 2007, any hopes of junction 31 finally being built were dashed when Cardiff Council denied the planning application and renewed plans for the Thornhill interchange were abandoned.
Junction 8/9 near Maidenhead, Berkshire, and High Wycombe, Buckinghamshire is the only one in the UK with dual numbers. This arose at the time when the M4 turned north near junction 8, where it met the A308, and headed for the original junction 9, where the motorway ended at a roundabout interchange with the A4.