Two alternative routes were investigated for this Section of the M56.
It had always been envisaged that it would cross and join the M6 at the already constructed A50 Interchange (J20), at Lymm. However, it was later recognised that the capacity of this junction, and of Thelwall Viaduct, would be future problem areas for the traffic growth which was expected.
A new 'motorway to motorway' interchange sited further to the south was, therefore, considered. In due course, the route which was published, as the first stage in the statutory procedures, provided for the connection with the M6 approximately 3000 feet south of the existing A50 Interchange.
The Scheme which was the subject of a Public Inquiry held in July 1970 provided for the construction of the 11½ miles of dual three-lane carriageway motorway; the completion of the interchange at Preston Brook; an interchange at Stretton to connect with A49 and A559; the interchange with the M6; and slip roads to connect to A556 at Bowdon.
As the Warrington New Town Development Corporation envisaged a new north-south road joining the M56 at Stretton, is supported the proposals
The route passes through agricultural land and the former Stretton Airfield. It was located to avoid property. Demolition was limited to two cottages, a disused chapel which was being used as a potato warehouse, and a gatehouse/bungalow.
The Cheshire Plain which it crosses, is generally well-covered with boulder clays and their associated 'middle' sands. Keuper Waterstones approach the surface in places. It was expected that, in the deep cuttings which would be required to achieve the designed vertical profile, the sandstone, siltstone and mudstone would be reusable, if protected from the weather.
The new Lymm Interchange was designed without a direct free-flow motorway link from M6 south, to M56 east, and vice versa. East bound traffic would be signed to leave the M6 at Tabley, the next junction to the south, and travel along the A556 to Bowdon. Movement in the reverse direction would use the same route.
Of the 26 bridges required for this length of motorway, 21 were designed with a similar type of deck using prestressed precast concrete beams. The edge beams are 'troughs', and on the overbridges these were to be used as service bays. A novel feature was the use of precast concrete parapet plinths which almost entirely eliminated the need for temporary formwork.
The bridge with the longest span was to carry the motorway over a slip road. With a large skew, and sight-line requirements, a 108 feet span was required, which was a length in excess of the maximum for a beam transported by road. A design for a simply supported post-tensioned concrete deck of cellular construction, was therefore adopted.
Following a further Public Inquiry into the Compulsory Purchase Order, a favourable decision was given.
The construction of the motorway was to be carried out under two contracts, with the boundary along the eastern boundary of M6. Alternative tenders were invited for rigid, composite and flexible carriageway construction. In each case, the accepted tender provided for fully flexible construction, and work began in October 1972 on both Contracts.
The excavation in cuttings produced sufficient suitable material for the embankments and the design allowed for the use of the better materials at formation levels. The Waterstone was, therefore, placed as a subgrade layer on embankments, and in some cuttings, to a minimum construction depth of 18 inches. This construction depth provided enough protection of frost-susceptible materials. Extensive landscaping was included in the Contracts, using excavated unsuitable materials, shaped and mounded throughout the scheme with particular attention to the Lymm and Bowdon Interchange areas.
The motorway between M6 and Bowdon was opened to traffic in December 1974, followed by Preston Brook to the M6, in July 1975.