The A249 Stockbury to Sheerness project is a Design, Build, Finance and Operate (DBFO) contract which the Highways Agency awarded under a PFI contract in 2004. The project involved the construction of the 5km long A249 Iwade Bypass to Queenborough Improvement. This scheme provides a new high level fixed link crossing of The Swale (the waterway between the Isle of Sheppey and the mainland) and will extend the existing dual carriageway road northwards to Queenborough.
Prior to this project the only road access to the Isle of Sheppey was via the existing A249 trunk road, which is carried by a lifting bridge over The Swale estuary. This bridge also carries the only railway link between the mainland and the island. Since marine traffic on The Swale has right of way considerable delays arose when the bridge is raised. The new high level Swale Crossing eliminates these delays, improving access to the Isle of Sheppey and fostering improved and sustainable growth in the area.
The capital cost of the project was approximately £79 million. Financial Close was achieved in early 2004 and the operation and maintenance of the whole route is undertaken by the Project Company under a concession contract until 2034.
The scheme includes a new high level crossing of The Swale (known locally as The Sheppey Crossing); the bridge is tall enough for ships to pass beneath it without disrupting traffic flows. The Kingsferry Bridge has been retained for use by local traffic. Construction of the project was undertaken by Carillion who in turn used Cass Hawood for the design of the Sheppey Crossing and Fairfield Mabey as their steelwork fabricator and erector.
Sheppey Crossing is a 19 span composite plate girder bridge which is around 1,200 m long. It required around 10,000 tonnes of steelwork and was constructed using the launching method, whereby the deck was constructed and ‘pushed’ out across the supporting piers.
A challenge for the contractor and the designers was the local ground conditions which included weak highly compressible Alluvium, containing layers of peat. Historical road construction had encountered problems associated with settlement and this had to be taken into account in the road design. Analysis suggested that up to 800mm of settlement could occur and the works were scheduled to allow this to take place without affecting the finished design.
The project was opened to traffic in September 2006.