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The beast of Bodmin tamed

Highways - Relieving the congestion hell that is Cornwall's A30 is calling for some inventive thinking. Mark Hansford reports from Bodmin.

Visitors to Cornwall rarely want to leave - they are seduced by the county's spectacular beaches and rugged cliffs. But that is not the whole story: The thought of enduring a return journey along the A30 is enough to make anyone want to stay put.

The 11.5km section of the A30 between Bodmin and Indian Queens is quite simply substandard, even by single carriageway standards, let alone for a road that carries 30,000 vehicles a day during the summer peak. Because the road is the county's principal artery it is pretty busy in winter too - 25,000 vehicles a day crawl along it.

Queues at weekends routinely stretch for miles for no reason other than sheer weight of traffic.

But by summer 2007 such queues should be a thing of the past, with work now getting into full swing to upgrade the section to dual carriageway via largely offline widening. While the work is carried out, contractor Alfred McAlpine has a cunning plan to ensure that nothing adds to motorists' woes.

McAlpine is carrying out the £59.7M job for the Highways Agency under an early contractor involvement (ECI) contract. It recruited Scott Wilson as its designer and worked up a way of building the road without putting construction traffic onto the clogged section.

'The big issue for us was how to construct a road where the existing route is at a standstill in the summer, ' says McAlpine project manager Keith Titman.

'Currently there are embargoes in place all summer restricting our use of the A30. But that is our busiest time.' Offline widening was the only realistic solution, with the existing road cutting through the Goss Moor Special Area of Conservation (SAC). 'The law requires any scheme that affects a SAC - including widening of an existing route - to consider any alternatives first, ' says Scott Wilson project manager Peter Colliver. 'So the only way forward was to bypass it to the north.' Towards the eastern end of the 11.7km scheme, however, the new dual carriageway will cross the existing road twice, at Victoria Junction and Innis Down Junction (see map). Some 1Mm 3 of material must be removed and taken west to where it is needed as fi ll. This involves transporting it past the two crossings and across a deep valley.

It is here that ECI came into its own. 'Because we weren't constrained from day one we started looking at how to get the cut and fill balance right and to deal with day to day traffic management, ' says Titman.

The broad plan is to create a temporary diversion for the A30 as far as the village of Holywell, creating a free run west for construction traffic.

To do this, a link road must be built to the north of the existing Mount Pleasant underpass and connected to the A30 by building the new Victoria Junction.

Construction of the new Innis Downs Junction underpass will allow traffic to turn onto the A391 without coming into contact with earthmoving plant.

Fortunately the existing roundabout at Innis Downs Junction is large - it was built with future widening in mind - and there is space in the middle to build the underpass as top down construction. This means that in the early stages a minimum amount of earth needs be excavated - just enough to drive piles for abutments, lay steel beams on top and place a composite concrete deck on top of that. Once that is done traffic can be put over the bridge and the material beneath excavated.

Getting these three elements in place has been the biggest priority this summer. 'Key to the programme at the moment is making the best of the good weather to get Innis Downs, Mount Pleasant and Victoria Junctions finished for the start of the earthworks season next year, ' says Titman. 'Which then gives us a free run to Holywell.' It is here that the next problem will be encountered - the deep valley. The cut-fill balance has been calculated exactly and the material excavated from Innis Downs is needed to create the new road west of Holywell. A viaduct was originally conceived to span the valley, but McAlpine quickly realised that extra land would be needed for cranes. It would also block the movement of material. So instead some of the cut from Innis Downs will be used to build up a steep, 15m deep embankment, working from the inside out.

'And that's the essence of being able to build the team up early, ' says Titman. 'The solution may not have come out and it would have added to the cost.

We would have tendered for a viaduct, and we would have built a viaduct, ' says Titman.

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