These were detailed in the "Greater London Development Plan", produced by the GLC in 1969. Some of the new roads had already been built, or were under construction, such as the Westway.
The plans consisted of a series of three concentric rings: in order of increasing radius Ringway 1 (also known as the Motorway Box), Ringway 2 (Abercrombie's C ring), and Ringway 3 (Abercrombie's D ring). The Outer Orbital Road (later to become the M25) was also mentioned, although since this lay outside the GLC's boundaries, this was the MoT's responsibility. Linking these orbital motorways would be a number of radial motorways: for example the M1 would be extended to meet Ringway 1.
The timescale for the plan was fairly long -- the North Cross and South Cross Routes of Ringway 1 were not expected to be built before 1980.