M25 motorway the east of Gravesend and Grays, the Lower Thames Crossing, in order to relieve congestion on the A282 Dartford Crossing and connect the M25 at North Ockendon in Essex with the M2 in Kent. At Junction 5, the clockwise carriageway of the M25 is routed off the main north–south dual carriageway onto the main east–west dual carriageway with the main north–south carriageway becoming the A21. In the opposite direction, to the east of the point where the M25 diverges from the main east–west carriageway, that carriageway become the M26 motorway. The radial distance from London (taken as Charing Cross) varies
M25 motorway began in 1973. The first section, between South Mimms and Potters Bar in Hertfordshire (junction 23 to junction 24) opened in September 1975 and was given the temporary general purpose road designation A1178 (a section of motorway-standard-road, originally the M16, which eventually was incorporated into the M25) was completed and operational before this. A Watford-avoiding route between the M1 and the A40 between north Watford and Denham was locally known as the Croxley Green/Rickmansworth bypass, and was operational about 1973/4; a section south of London (junction 6 to junction 8) opened in 1976. A section of Ringway 3 south of