Highways England makes case to build world’s longest road tunnel

A tunnel under the Pennines to provide a new road link between Sheffield and Manchester is technically feasible and worth exploring further, according to Highways England engineers.

At between 20km and 30km, potentially, it could be the world’s longest road tunnel, but it could be done, and could potentially deliver economic benefits of up to £421m a year, initial studies suggest.

In July 2015, the Department for Transport and Transport for the North (TfN) jointly commissioned Highways England to assess the feasibility of a new strategic highway route connecting Manchester and Sheffield across the Pennines. The government and TfN believe that an improved transport corridor between Manchester and Sheffield could improve the economic prosperity of both cities and the wider Northern Powerhouse region.

Highways England’s interim report has now been published1. Among its conclusions it says:

objectives for the road scheme align with government policy and there is a case for change as part of developing ambitions for a Northern Powerhouse

constructing a new route between Manchester and Sheffield across the Pennines is technically feasible, although the most effective route options are yet to be considered

operating and maintaining the new road link — a considerable proportion of which could be in-tunnel — presents significant challenges, but is feasible in principle

while early findings are positive, further work needs to be carried out to develop the economic case.

The two longest road tunnels in the world are: Laerdal Tunnel (one bore of 24.5km) in Norway, which opened in November 2000; and Zhongnanshan Tunnel (two bores each 18km) in China, which opened in January 2007. The experiences and knowledge gained from constructing these long road tunnels are being applied to this study.

On the technical issues, the report says: “The construction of a new strategic road link involving a substantial length of tunnel is technically feasible. Modern tunnelling techniques can accommodate a dual carriageway tunnel and the geology of the Pennines is generally suitable for constructing large diameter ores. Various tunnelling methods are available, including the use of TBMs for diameters up to around 15 metres, drill-and-blast techniques and, potentially, cut-and-cover sections. We will consider the cost and environmental impacts of these tunnelling methods for each potential route option.

“The construction of overland sections at either end of the tunnel and on the fringes of the National Park to connect the new route with the strategic road network presents a number of technical challenges but is technically feasible.

“The tunnel is likely to be longer than most other road tunnels in Europe, and the psychological aspects of travelling through a tunnel of this length are broadly understood. However, it is appreciated that we will need to undertake further work to understand driver behaviour and to consider how advances in technology and appropriate tunnel design could help to mitigate this issue.”

The economic case is less certain: “We have carried out a very high level illustrative scenario modelling of productivity effects on business from better links between Sheffield and Manchester. These scenarios show productivity benefits of between £171m and £421m per annum, with further potential gains of productivity arising from increased competition across markets. However these are just scenarios and benefits maybe higher or lower when actual data has been analysed.”

It also says: “Based on the work carried out so far there is a good case for further work but more modelling will need to be done before we are in a position to reach a conclusion about the full case for investment in a tunnel.”

The case for a trans-Pennine road runnel will now be examined by the new National Infrastructure Commission (NIC)2, whose chairman, Lord Adonis, said: “The NIC will assess all the evidence and provide independent advice to government on the future priorities to improve connectivity amongst the great cities of the North, and this report will form an important part of that review.

“For too long, the British people have had to suffer from the delays, congestion and excessive journey times caused by successive governments failing to plan long term on big infrastructure projects. It’s time for a new approach, building broad consensus behind a long term plan backed up with serious and sustained investment. That is what the National Infrastructure Commission will help create.”