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Busting the bottleneck

In high summer nearly 30,000 vehicles a day grind along the single carriageway A249 north of Iwade, heading to and from the Isle of Sheppey, on the south side of the Thames Estuary. Much of this is holiday traffic, but there is a sizeable proportion of HGVs, mostly servicing the busy port of Sheerness. South of Iwade the A249 is a modern dual carriageway link to the M2 and M20. The last few kilometres of overloaded, unimproved road represent a major bottleneck, one that threatens the future economic and social development of the island.

Congestion and delays are made even worse by one special factor. The Kingsferry Bridge, the only crossing over the tidal Swale passage between the island and the Kentish mainland, was built some 45 years ago as a combined road and rail bridge, limiting its maximum gradient.

To cope with the low banks on either side and the busy maritime traffic on the Swale, it was designed as a lift bridge, the only one of its type on the UK highways network.

'The problem is that traffic volumes on both the road and the Swale have increased dramatically over the last few decades, ' explains Highways Agency project manager Graham Link.

'A lift can mean a 15 minute road closure. When peak road traffic coincides with high tide - the peak time for maritime traffic - disruption is considerable.' Commercial as well as pleasure craft use the Swale.

The only realistic option was a high level bridge. Rail authorities decided they could live with the lift bridge's disruptive effects on what is essentially a branch line, meaning that steeper approaches to the crossing were possible, minimising cost and visual intrusion. A compensation area has been created on the mainland to make up for wetland lost to the works.

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