Contract 4 was split into two sections. Contract 4A (valued at £8m) extended northwards from the Bishop's Stortford interchange (junction 8) to near Quendon and was undertaken by Sir Alfred McAlpine (Southern) Ltd. The contractor for Contract 4B (valued at £9.8m), which extended from Quendon to the Stump Cross interchange (junction 9) was Holland Hannen and Cubitts (Civil Engineering) Ltd (later bought out by Tarmac (now Carrilion Construction)).
Both contracts, totalling 24 km, included dual two-lane concrete carriageways 7.3m wide with 3.5m hard shoulders. A further 0.7km long link connected the M11 motorway with the Cambridge Western Bypass.
Earthworks were predominantly in boulder clay and chalk, with this latter material being confined to Contract 4B and constituting approximately 50 per cent of the total excavation in that contract. Due to the presence of water-bearing gravel lenses and water permeation at formation level in cuttings it was necessary to excavate 400,000 cubic metres of more suitable filling material from local 'borrow' areas.
The route traverses an area of rolling downland, requiring sensitive environmental treatment because of the high quality farmland and scattered village communities. To take account of these constraints, and at the same time achieve a flowing alignment, radii generally between 1312m and 2755m were used in conjunction with gradients not exceeding 3.8 per cent. The cuttings and embankments reached maximum depths and heights of 11.5m respectively below and above motorway level. The Department of Transport later carried out tree planting and other landscape work, and the contracts included extra deep soiling at selected locations for this purpose.
The excavation of cuttings and the formation of embankments required the handling of over 3.9 million cubic metres of boulder clay, gravel, silt and chalk material. Due to the high water table and water-bearing layers encountered within the clays, only about 70 per cent of the three million cubic metres excavated could be used for embankment construction and this was supplemented by 400,000 cubic metres of material excavated from drier 'borrow' areas to complete the embankments and to replace waterlogged ground adjacent to stream crossings and beneath the road formation in cuttings. The slopes of cuttings and embankments varied from 1:1½ to 1:3 consistent with materials stability, with cutting stability being augmented by slope drainage in various locations.
There were 29 structures, including bridges of various types, in the two contracts. Most of the M11 bridges were built to standard 'type' designs, and therefore many of the bridges on contracts 4A and 4B were similar to designs already built on the completed sections of the motorway. In this manner a visual interest is maintained by varied appearance with individual sites defining the particular 'type' requirement.
Except where horizontal curvature prevented the use of a central pier, motorway overbridges were normally four span, being either constant depth spans or with variable depth motorway spans more suited to super-elevated carriageways. Within these 'type' designs varying finishes were applied together with varied forms of pier construction to provide further visual contrasts. Underbridge types were either rectangular or, in order to counter the 'tunnel' effect, had sloping walls.
Farm accommodation, foot and bridleway bridges occured in several different forms to suit the individual locations and to further increase the 'interest' factor.
