Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Should tunnels replace our aging bridges?

Discovery of an additional crack in a critical section of the Boston Manor viaduct has once again placed the civil engineering and highway maintenance industry under the media spotlight. But while the main focus was initially on how quickly the repairs could be completed, civil engineers and asset owners need to consider the broader issues this has raised – should we be looking for a short-term fix or investing in long-term replacement of such structures?

The main outcry over Boston Manor, which reopened last week has centred on how this could happen again so soon after the similar recent closure for repair of Hammersmith flyover. The fast-approaching start of the London 2012 Olympics has also upped the ante. But the media coverage has paid little attention to the fact that the structures fall to the responsibility of different road operators.

Like for like?

They are also unique in their own right, and so their structural problems cannot be directly compared.

But what the structures do have in common with each other – and with many other parts of the UK transport network – is their age, and the fact that they now carry traffic volumes that were never anticipated when they were designed.

The current solution for these structures appears to be mend and make do in a bid to get them back to work as quickly as possible. But is this the right approach?

Halcrow global head of tunnelling Martin Knights believes the industry must think much further ahead. “Civil engineers need to be more proactive and use their technical knowledge to look for solutions and approach clients directly rather than waiting for instructions,” he says. Knights is part of a team from Halcrow working with Hammersmith-based Chartered Practice Architects to champion replacement of the Hammersmith flyover with a new tunnelled “flyunder” alternative.

Hammersmith flyunder?

Knights says the concept has been used successfully on the M30 in Madrid and the principles are also being applied to the Alaskan Highway in Seattle. Up to half the cost of the $4bn (£6.4bn) project in Seattle has been funded by selling off land freed up by the new tunnelled route. Knights says the same approach could be used at Hammersmith.

Knights stresses that the scheme is still a concept at this stage and must gain public support before the technical detail is worked out.

“If we can deliver a technical solution to the scale of tunnelling needed for Crossrail, then we can engineer a solution for Hammersmith too,” he says.

Although Transport for London has recently gone out to tender for the next phase of rehabilitation works for the Hammersmith flyover, which it says will extend the service life by 100 years, the local authority is behind the search for an alternative. London Borough of Hammersmith and Fulham council leader Nick Botterill is fully in favour of the tunnel concept.

“There is no scheme of replacement currently being planned, however, it is our strong view that this needs to be looked at starting now,” he said. “Is it really a good policy to keep patching up a 50 year old structure, which has declining resilience and capacity at ever more considerable cost?

“While construction would take a number of years, the benefits of a tunnelled replacement would be considerable. The whole area would be reunited with the riverside which would also have profound economic and environmental benefits.” Knights believes that the scheme is viable and that other infrastructure problems in urban areas of the UK could be dealt with in a similar way.

Diversion aversion

Maybe this is the right approach for the road network where diversions while construction takes place are relatively simple – but what about for rail?

A recent visit by staff from French rail firm SNCF to the UK to compare and contrast its network management with that of Network Rail brought exactly those issues to the fore. The discussions highlighted Network Rail’s preference for significantly increasing spend on earthwork structures maintenance to reduce the need for investment in large scale schemes. However, the emphasis placed on planning this maintenance by Network Rail head of civils asset management (geotechnics) Tony Wilcock suggests that this approach falls somewhere between mend and make do and long-term reconstruction.

How the programme will be achieved is a diff erent matter but another interesting fact that came out of the visit is that French rail users are far more accepting of temporary line closures to allow work to be completed. This automatically makes rail work cheaper in France as SNCF is not paying overtime rates for staff working over bank holidays.

So do UK road and rail users need to come to terms with closures and diversions on a more frequent basis as existing structures are repaired?

The answer is probably yes – if we continue with the mend and make do approach, these closures and diversion could be sudden but maybe shorter in duration. If we take the long term replacement approach, the work could take longer, but the impact could be planned for and the potential for future emergency work reduced.

There is no easy solution but it is one that needs to be considered by UK infrastructure providers.

Readers' comments (2)

  • "Flyunder"? What is wrong with underpass?

    Unsuitable or offensive? Report this comment

  • Well, there's nothing wrong with underpasses/ flyunders except that extremely long ones are expensive and have significant safety risks in comparison both in construction and in operation.

    Unsuitable or offensive? Report this comment

Have your say

You must sign in to make a comment.

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.