Johnson’s plan for bridge or tunnel in Irish Sea rejected by official inquiry | Transport policy

Boris Johnson’s proposal for a bridge or tunnel connecting Scotland with Northern Ireland has been rejected by a feasibility study as hugely expensive and fraught with potential difficulties.

Published in conjunction with a broader so-called union link review, which called for investment in road, rail and domestic flights to better connect the four British nations, the Fixed Link report found either a bridge or tunnel would be on the edge of what could be achieved with current technology.

The estimated cost of the bridge would be £ 335 billion. and £ 209 billion. for the tunnel, where the latter is only able to accommodate trains for safety reasons. It would take at least 30 years for one of the links to open.

A particular problem that was raised by engineers when Johnson proposed the connection in 2019 is Beaufort’s Dyke. The seabed trench is up to 300 meters deep and more than two miles wide at its widest point, and it is also filled with millions of tons of ammunition dumped in the 1970s.

A tunnel is to be built at depths of about 400 meters below the water surface, which exerts considerable pressure and requires a rise of 25 miles in both directions given a maximum rail gradient of one in 100.

By comparison, the Channel Tunnel is just over 23 miles long with a maximum depth of 75 meters.

Beaufort’s Dyke would also prove to be “a challenge” for the bridge because the construction had to pass over the trench with a span of at least 2.5 miles and foundations set back from the edge, said the study, which was led by a small team of civil engineering experts.

No suspension bridge with such a long span has yet been built, the report said, although there have been some design concepts with similar lengths.

In an introduction to the feasibility report, Sir Peter Hendy, chairman of Network Rail, who led the link review, said the study had concluded that both projects were possible.

“However, a bridge crossing would be the longest bridge built to date,” he wrote. “A tunnel would be the longest underwater tunnel ever built given the limited inclines that trains can run on, the route it must take and the depths it must reach.”

Building a rail link would also create “some complexity” because the gauge in Northern Ireland is the same as in the Republic but different from the rest of the UK.

Hendy, who headed Transport for London when Johnson was mayor of the city, nevertheless said it had been “excellent questions to ask”.

He wrote: “For many decades, politicians and engineers have debated this proposal, but have done so without evidence to show if it was possible, and if so, what it would take to do so. This is the first comprehensive, crucial study on the subject since the idea was first put forward over 150 years ago. “

Johnson has a mixed record in terms of proposals for ambitious bridges. As mayor of London, he spent at least £ 37 million on public money on a planned garden bridge over the Thames despite concerns about funding, the project’s purpose and the lack of planning permits on one side of the river.

Among the ideas in the broader connection review was investment in the west coast railway line north of Crewe to provide better connections to Scotland, something that goes beyond the € 96 billion railway plan. pounds, which was announced last week, and an upgrade to the A75 road, which runs from the M6 ​​near Gretna Green to the Scottish ferry port of Stranraer.

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