The M16 motorway was the designation planned in the late 1960s and early 1970s for use on

Ringway 3 The London Ringways were a series of four ring roads planned in the 1960s to circle London at various distances from the city centre. They were part of a comprehensive scheme developed by the Greater London Council (GLC) to alleviate traffic con ...

, a new motorway planned as part of the London Ringways Plan to run a circular route around London. Construction of the first section of the M16 began in 1973 between South Mimms and Potters Bar in

Hertfordshire Hertfordshire ( or ; often abbreviated Herts) is one of the home counties in southern England. It borders Bedfordshire and Cambridgeshire to the north, Essex to the east, Greater London to the south, and Buckinghamshire to the west. For govern ...

and opened in September 1975 with the temporary general purpose road designation A1178. During construction of the first section of the motorway, the majority of the Ringways plan was cancelled and, in 1975 the plans for Ringway 3 were modified to combine it with parts of another motorway, Ringway 4, the outermost Ringway. The M16 designation was dropped and the combined motorway was given the designation M25 which had originally been intended for the southern and western part of Ringway 4.The section of Ringway 3 west of South Mimms anti-clockwise around London to Swanley in Kent was cancelled and the section clockwise from Potters Bar to the

Dartford Tunnel The Dartford-Thurrock River Crossing, commonly known as the Dartford Crossing and until 1991 the Dartford Tunnel, is a major road crossing of the River Thames in England, carrying the A282 road between Dartford in Kent in the south and Thurro ...

was constructed between 1979 and 1982. The section of Ringway 3 south of the river between Dartford and Swanley was constructed between 1974 and 1977. The South Mimms junction was originally intended to be the end of a short spur connecting the A1 to the M16. The main alignment of the M16 would have continued south-west of the junction towards

Radlett Radlett is a village in Hertfordshire, England, between Elstree and St Albans on Watling Street, with a population of 8,042. It is in the council district of Hertsmere in the south of the county, and is covered by two wards; Aldenham East and ...

and Bushey. Evidence of this unbuilt alignment remains in the wide gap between the carriageways to the east of the South Mimms junction which would have been the point at which the spur would have separated from the continuing carriageway.

References

{{DEFAULTSORT:1-0016 Former motorways of the United Kingdom Geography of the London Borough of Enfield Hertsmere London Ringways M25 motorway Motorways in England Roads in Essex Transport in the London Borough of Enfield Roads in Hertfordshire