The M6 motorway is the longest motorway in the United Kingdom. It is located entirely within England, running for just over 230 miles (370 km) from the Midlands to the border with Scotland. It begins at Junction 19 of the M1 and the western end of the A14 at the Catthorpe Interchange, near Rugby before heading north-west. It passes Coventry, Birmingham, Wolverhampton, Stoke-on-Trent, Preston, Lancaster and Carlisle before terminating at Junction 45 near Gretna. Here, just short of the Scottish border it becomes the A74(M) which continues to Glasgow as the M74. Its busiest sections are between junctions 4 and 10a in the West Midlands, and junctions 16 to 19 in Cheshire; these sections have now been converted to smart motorways. It incorporated the Preston By-pass, the first length of motorway opened in the UK and forms part of a motorway "Backbone of Britain", running north−south between London and Glasgow via the industrial North of England. It is also part of the east−west route between the Midlands and the east-coast ports. The section from the M1 to the M6 Toll split near Birmingham forms part of the unsigned E-road E 24 and the section from the M6 Toll and the M42 forms part of E 05.
