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 and round and curvy like design. On the elevated ground between Shap and Tebay, the north and south-bound carriages split apart. At this point a local road (to Scout Green) runs between the two carriageways without a link to the motorway. The section of the M6 that runs over Shap Fell in Cumbria is above sea level, one of the highest points on any motorway in the UK (junction 22 of the M62 on Saddleworth Moor is higher). The motorway engineers here chose to follow the route of the Lancaster and Carlisle Railway engineered by Joseph Locke (now part of