 The section in West London was eventually built to a lower standard as the A312.Ringway 3 was planned to link the capital's outer suburbs linking areas such as Barnet, Epping, Dartford, Purley and Chessington.Construction began on the first section of the motorway between South Mimms and Potters Bar in 1973 and the motorway was initially designated as the M16 motorway before its opening.