The UK is contemplating the pros and cons of constructing the world’s longest road tunnel. Not yet named, it would be an improvement of the A628 connection between Sheffield and Manchester, located in the Peak District, a hilly National Park in the North of England. Alex Conacher, editor of Tunnels & Tunnelling magazine, examines the potential project.
A particular part of this 61.5km road traverses the Woodhead Pass, which because of its elevation and exposure, is subject to high winds and snowfall during the winter months.
The tunnel itself (although it could yet be a series of tunnels) is reported to cost of the order of GBP 6bn (USD 9bn), with a bored length of up to 30km. However, the lower estimate of 20km would see it drop below the length of Norway's 24.5km Lærdal Road Tunnel, which opened in 2000.
An interim report observed that the diameter of tunnel bores would be limited to 15m by "present day TBM technology". Geology would largely comprise rocks of the Millstone Grit and Pennine Coal Measures groups, and would be relatively consistent throughout study areas (the Woodhead Railway Tunnel can be considered a precursor project in geological terms). In addition, the topography would mean the tunnel would have to relatively deep.
The report, published last month, concluded that more study was needed, and that a more detailed report would be produced late in 2016. It identified the main benefit: the weatherproofing of the route, as well as getting 30 minutes knocked off the current journey time.
The report also uses the phrase 'Northern Powerhouse' a number of times - which is the current buzzword of the Chancellor of the Exchequer's plans to rebalance the UK economy away from London.
More interestingly, a lot of the details of the tunnel are still undecided. One of the findings of the report was that "the development of a combined road and rail corridor through the tunnelled section could offer some additional benefits, although road and rail would need to occupy separate tunnel bores and we have not yet established the operational case for this type of solution".
So this tunnel really could look much different from a single road tunnel when it comes to the final design, and could end up being quite an ambitious scheme if it goes ahead. Even reaching the remote worksite will be a challenge for teams. But the operational concerns may be the most interesting.
A 30km road tunnel goes considerably beyond anything else the world has seen. At this length, engineers will not only have to consider the usual problems of lighting and ventilation, but also driver boredom, claustrophobia, and fatigue. There are tunnels elsewhere in the world that have large cavern lay-bys for rest stops. However, with the volumes of traffic potentially passing through this route, this could be dangerous. Whether subterranean service stations will be required is also a question that will need to be addressed.
One of the final promises of the report was to commission UK-based research into driver behaviour, and a study of other long road tunnels worldwide.
* This article originally appeared in Tunnels & Tunnelling magazine: www.tunnelsonline.info