M25/History

Early Plans

Later Plans

Finishing the loop

After the collapse of the Ringway plans, the question of how to link the two half loops that were being built had to be answered. The motorway standard section of Ringway 3 would run from the A1 at Bignells Corner (and possibly still further west), to the M20 at Swanley Interchange, and Ringway 4 would be motorway standard from the M20 at Addington Interchange to the A41 at Hunton Bridge

In the South East

Two main options were looked at:

Provision of full access at Addington Interchange, with Orbiting traffic heading along the M20 to Addington and then back to Chevening Interchange along what is now the M26.
A new build route from Swanley to the A21 south of Orpington with an online upgrade of the A21 through Chevening Interchange.

There were sit in protests on the A225 to get the new build route built. The lengthy detour required by the other option meant that the A225, which at that point was primary due to its purpose in linking the two Kentish bits of M25 together, would be used as a rat run, not being adequately bypassed.

In the North West

Various options were looked at:

Offline route between the Hunton Bridge area and The Bell Roundabout, avoiding urban areas, then an online upgrade of the A6 to Bignells Corner. This option was chosen.
Offline route between the Hunton Bridge area and Park Street Roundabout, then an offline upgrade of the A405 and an online upgrade of the A6 to Bignells Corner
Online (or near enough) upgrade of the A41 between Hunton Bridge and Berrygrove (at that point still due to be upgraded to A41(M)), then a variety of options to get to Bignells Corner:
- Extension of Ringway 3 to the M1 along the original plans, leaving a short M25/M1 merger from Berrygrove to Bushey Interchange
- Construction of the Stirling Corner Link and upgrade of the A1 to motorway, meaning orbital traffic would head south along the M1 to Scratchwood Interchange then north to Bignells Corner.

Some options were not mutually exclusive, for instance the southern option, may have been paired with an M10 extension to Bignells Corner along the A405 and A6. Likewise both M1-A1 options may have happened, with the A1 route simply A1(M).

Northern Route Junction images

The M25 northern route option's junctions with the M1 and M10
Park Street Roundabout with offline upgrade of the A405 route
London Colney Roundabout with offline upgrade of the A405 route

Construction

This is the layout of the M25 between J6-8 as it was in 1978

Improvements

Orbit study

In 1989, the Orbit study looked at the M25 and the traffic on it. Upgrading parallel roads - eg A312, A331 and A404 - was recommended, and mostly carried out. Also recommended was a large amount of widening to D4M and further with collector-distributor roads. The study had this table of how wide the traffic would require the road to be: