M55 motorway meet junction 4, where the motorway ends and becomes the A5230. The western part of the M55, and the first few hundred metres of the A5230, occupy the route of the old Blackpool Branch railway line. The first motorway constructed in Great Britain was the M6 Preston Bypass, opened in 1958. This ran from the current M6 junction 29 to the M55 junction 1. It was built as a two-lane route. In 1965 the M6 was extended north from what is the current day junction 32 to meet the Lancaster Bypass, and the M6 junction was rebuilt to its current
M6 motorway 1970, the Lancaster–Penrith link was completed, along with a short section of motorway by-passing the south of Walsall. The most northerly section of the motorway also opened in 1970, running to the designated terminus north of Carlisle. By 1971, the full route was completed between the junction with the M1 motorway at Rugby and the A38 road several miles north-east of Birmingham city centre, including Bromford Viaduct between Castle Bromwich (J5) and Gravelly Hill (J6), which at 3½ miles is the longest viaduct in Great Britain. Junction 6 in Birmingham is widely known as Spaghetti Junction because of its complexity