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Costain tackles tunnel trouble

ROADS AND BRIDGES - Of the many bottlenecks which clog up the trafc on the M25, London's orbital motorway, the Holmesdale Tunnel near Waltham Abbey to the north of the capital is one of the worst. Alasdair Reisner discovers how Costain is getting the traf

TO DRIVERS it is sheer agony. The M25 motorway circling London is a road to Hell, a snarling ring road of bumper-tobumper traffic chugging around the outskirts of the capital, often seizing up as accidents or overuse bring it to a halt.

So anyone who might help reduce this congestion might expect the eternal thanks of M25 users.

Enter the Highways Agency and contractor Costain. The pair are leading a team that has been tasked with sorting out one of the route's most notorious blackspots; the Holmesdale Tunnel.

The tunnel and nearby Junction 25 were identified as a priority junction action site in October 2002, requiring work to upgrade it from two to three lane dual carriageway to reduce congestion.

While the westbound carriageway was upgraded in 2002, the team could only now widen the eastbound carriageway. The mechanical and electrical systems in the tunnel are also at the end of their design life, having been in constant use since the tunnel opened in 1984. Clearly intervention was required to prevent future traffic problems.

But the road to redemption is not an easy one. Highways Agency project leader Eamonn Colgan is under no illusions as to the scale of the challenge the team faces.

'This is the busiest part of the busiest motorway in the UK, ' he says. 'There may be more traffic on the M25 at Heathrow but there are more lanes there. It is a massive undertaking. It is not something we take lightly, ' he says.

The tunnel doesn't just set domestic records. With 120,000 vehicles using it each day the tunnel is, in fact, the busiest on the Transeu ropean road network .

The irony for Mr Colgan is that in trying to carry out works to reduce congestion, the project could run the short-term risk of increasing it. But he says the team is doing everything in its power to make sure this is not the case.

'We were going to have to close some slip roads to junction 25 for 18 months so we needed to inform the stakeholders. We had a massive publicity campaign, working with the local highway authorities, the RAC and the freight haulage associations. There were ads in the Evening Standard to tell people when the works where going to start. We even took cinema ads at the nearby UCI at Waltham Cross. We had enormous feedback. We told people that if they don't need to use the area, they shouldn't.'

'Although we saw a little bit of congestion on the local roads in the first couple of weeks it was quick to calm down. The roadworks are signposted all the way from Birmingham to Kent so people know about them long before they arrive here. All of these methods together are what has kept the traffic moving.'

The scheme was procured using the Highways Agency's early contractor involvement model. Although the scheme did not have to go through a public inquiry - when a contractors input can shave weeks or months off the delivery programme - Costain still managed to use its knowledge to make the job more efficient with another major congestion-busting measure. With the firm's input the length of traffic management required for the scheme was slimmed down from 5.2 km to just 2.8 km.

'The feedback is that it has bedded in well. The big benefit of the ECI approach was in the buildability and efficiency of the scheme rather than managing through 'optioneering'. We have maintained our programme and produced a far more buildable solution, ' says Darren Jones, Costain's highways director.

But with such efficient running, surely there isn't a great deal of slack in the system if things go wrong? Surely if someone breaks down the whole area becomes a bottleneck and traffic grinds to a halt. Not so, according to Mr Meadowcroft.

'We don't have any hard shoulders so if people do break down there are five vehicles placed at strategic places to go out and quickly get them off quickly, ' he says. 'There is a total package there to make sure they are treated well. We aim to get there in 10 minutes and recover by 20 minutes.'

The work itself started in March this year. The first stage was scheduled to last 17 weeks and involved installing traffic management to create an 'island' around the central wall that runs down the middle of the tunnel, separating the opposing lanes.

When the tunnel was constructed this had been built with walkways to allow anyone stuck in the tunnel a safe way out away from traffic. But this no longer meets with current design standards so it has been demolished. The existing blockwork wall was also replaced with a reinforced version and two new fire doors were added to it, increasing the number of fire escapes between the tunnels from three to five.

It is testament to the planning work and the smooth running of traffic through the site that these works were actually completed four weeks ahead of schedule.

Once this was complete the team could divert all of the traffic out of the eastbound bore onto the westbound. Initially this had been planned to have two lanes of traffic in either direction but during value engineering the team realised it could actually squeeze in an extra lane, allowing three lanes in one direction to further reduce the congestive effects of the work.

With the traffic out of the eastbound tunnel the team is now at work inside, carrying out complete refurbishment. A second walkway on the outer wall has also been removed, freeing up space for the extra lane through the tunnel.

The new mechanical and electrical systems are being installed and the whole lining of the tunnel is being given a coating with a fireproof cementitious spray and reflective paint to bring more light into it.

At the same time the team has been working to build a 40 mlong, 1 m-thick, 8 m-high reinforced central wall at western portal to the tunnel, replacing an existing anti-circulation wall.

The larger central wall is part of the structure required to hold the ventilation system for the tunnels (see below).

In total the eastbound bore is expected to take around 24 weeks, after which the team will f lip the contraf low so that the traffic goes in it, allowing them to get to work on the westbound bore. Here the same M&E replacement and fireproofing will be carried out along with construction of a second fan station at the eastern portal. Again these works are expected to last 24 weeks.

The overall project is due for completion by September 2007, by which time the team will have made the journeys of thousands of motorists on the M25 each day just that little bit easier.