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Swale River Crossing

Swale River Crossing under constructionSwale Crossing
A249 Iwade to Queenborough Improvement/A249 Stockbury (M2) to Sheerness DBFO
The existing Kingsferry Bridge was until recently the only link connecting the Isle of Sheppey to the Kent mainland, carrying a railway as well as the A249 Trunk Road to the port of Sheerness. This structure's lifting span over the Swale (the channel separating the island from the mainland) allows shipping access to Ridham Dock to the east of the structure, as well as busy leisure use of the Swale. With ever increasing traffic, the limited capacity of the single carriageway road over the Kingsferry Bridge, coupled with the long delays resulting when the bridge was opened, led to the decision by the Highways Agency to provide a new structure to accommodate an upgraded A249, with the existing Kingsferry bridge continuing to accommodate the railway and a de-trunked secondary road alongside the A249.

The new scheme, known as the Iwade to Queenborough Improvement, was conceived and developed by Mott MacDonald and included a new dual carriageway passing over a 1270m long high-level fixed bridge with 29m air draught above the Swale – the same clearance as provided by the Kingsferry Bridge in its lifted position. The structure's 19 spans, supported on pairs of tapering circular columns, ranged from 44m at the abutments to 92.5m over the navigable span, with a proportionally increasing construction depth. The general form of the structure as presented to public inquiry (and later defined within the M249 Stockbury (M2) to Sheerness Design, Build, Finance and Operate (DBFO) Contract) was accepted by the Royal Fine Arts Commission, and its river pier positions, in conjunction with those of the nearby Kingsferry Bridge, were analysed by computer simulation to ensure that navigation in the Swale was not compromised.

Whitewell flyoverThe new crossing and its approaches are located within the North Kent Marshes, an extensive area of grazing marshes and inter-tidal channels/mud-flats, which are internationally important for migratory and over-wintering birds. The road corridor passes through sites of special scientific interest, special protection areas and a ramsar site - national, European and international designations indicating the environmental value assigned to the area. In order to avoid seriously damaging the habitats for which the area is so important, extensive consultations took place during the scheme's early development and the design as presented to Public Inquiry (and later incorporated into the DBFO Contract) was developed to take the absolute minimum of new land and to provide mitigation for the impacts of the existing as well as the new crossing.

The A249 Stockbury (M2) to Sheerness DBFO Contract involved the construction of the original Iwade to Queenborough scheme and includes the operation and maintenance of a more extensive length of the A249 over a concession period of 30 years. Following the initial development of the scheme, Mott MacDonald were retained by the Highways Agency to support them through the DBFO procurement process, and following contract award in February 2004 undertook a design review, auditing and construction monitoring role on behalf of the Agency. The bridge was constructed by incrementally launching (from each abutment) a steel girder composite deck into position over the Swale, and was opened to traffic in June 2006. The crossing has since been the recipient of a number of national awards.

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