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Introduction

Probably the decision which has had the greatest effect on the M5 in Worcestershire was to build it to dual 2-lane standard. It has to be remembered that the Gloucester Section (south of junction 8) was dual 3-lane and the section north of Quinton (junction 3) was dual 3-lane. There seemed no sense therefore in building the middle section in Worcestershire to dual 2-lane. Despite repeated representations from Worcestershire County Council, the Police and particularly the County Surveyor of Worcestershire that dual 3-lane standard was appropriate, The Ministry of Transport refused to budge and thus it became a dual 2-lane motorway. The short sightedness of this decision was to be brought home the hard way when it became necessary to widen the Worcestershire section of M5 at a cost of £123 million. The original 28 miles of motorway had cost just £8 million. Every bridge had to be demolished and rebuilt.

The widening and reconstruction was carried out over a period of about 15 years, and included a variety of widening approaches. This included widening within the existing highway boundaries, and new symmetrical or asymmetrical construction.

The section of the M5 between Junctions 4 (Lydiate Ash) and Junction 8 (Strensham) was designed to dual two lane motorway standards which are below those in current use. In layout, as an example, only 18% of the sight distances between Warndon and Catshill meet full current requirements.

When the design brief was started in 1980, the motorway was carrying 38,000 vehicles daily; by the start of construction in 1985 the flow had increased to 42,000 vehicles per day; it is currently exceeding 100,000 vehicles per day on the widened section south of M42.

The expected life of the carriageways was far less than 20 years when measured in current standard axle terms. Thus the reconstruction of the most distressed areas between Junction 6 and Junction 8 was commenced in 1977 and completed in 1983, well in advance of its eventual widening in the early 1990s.

Concurrently the planning of the combined reconstruction and widening of the remaining motorway between Junction 4 and Junction 6 was commenced. This scheme was divided into four Contracts at an estimated cost of £53M. The work involved the demolition of all the overbridges and the construction of replacement structures together with the extension and sometimes replacement of the bridges carrying the Motorway over roads, a railway, rivers and a canal. Improvements were also made to the Motorway alignment as some bends were too sharp and the whole width of the carriageway was rebuilt as necessary. Completing the M5/M42 junction was combined with the adjacent widening contracts.

Widening and reconstruction of 'live' motorway demands pre-planning and advance works far in excess of similar activities on green field sites. The provision of maximum traffic capacity on the motorway, coupled with working space for the Contractor and adequate diversion routes for traffic overspill are essential pre-requisites. As the highway authority for roads, other than motorway or trunk roads, the County Council was uniquely placed to assist the Department of Transport by ensuring that the optimum balance was achieved on the motorway and on the local road network, which carried both Contractors and diverted traffic. To achieve this objective, advance works costing £5m were carried out. These included improving diversionary routes, re-siting Statutory Undertakers equipment, restoring skid resistance to old carriageways, providing street lighting, strengthening hard shoulders, and providing central reservation crossings.

Comparison of the cross sections showed the dramatic change that had taken place in the build up of motorway furniture. The original empirical design performed extremely well structurally. Although superficially modernised into the intermediate two lane cross section with all the modern aids to movement and safety it still retained inherent weaknesses in alignment, visibility and drainage. Online widening made the updating of these deficiencies difficult but asymmetric widening over 25% of the scheme improved alignment and visibility. Fixed drainage outfalls created problems but drainage was improved considerably to form a more efficient drainage system.

The interpretation of Deflectograph, crack and soil surveys and compliance with DTp recommendations for pavement thickness, presented problems in marrying new to old pavement. The objective to retain as much of the existing pavement as possible was, in many cases, frustrated by the need to break out old hard shoulder, to meet level tolerances at existing underbridges and to produce an acceptable pavement combining both old and new design.