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

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

Released alongside a broader so-called union connectivity assessment, which called for investment in road, rail and domestic aviation to better connect the four UK countries, the fixed link report found that a bridge or tunnel would be on the edge of what could be achieved with current technology.

The estimated cost for the bridge is £335 billion and £209 billion for the tunnel, the latter of which can only accommodate trains for safety reasons. It would take at least 30 years for either link to open.

One particular issue, raised by engineers when Johnson proposed the link in 2019, is Beaufort’s Dyke. The trench on the seabed is up to 300 feet deep and over two miles wide at its widest point, and is also filled with million tons of ammunition dumped in the 1970s.

A tunnel would have to be built at a depth of about 400 meters below the water level, applying considerable pressure and requiring a 25-mile climb in either direction, given a maximum track gradient of one in 100.

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

Beaufort’s Dyke would also pose a “challenge” to the bridge, as the construction would have to go over the trench, span at least 4 miles and the foundations spaced from the edge, said the study, which was led by a small team of civil engineering experts.

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

In an introduction to the feasibility report, Sir Peter Hendy, Network Rail’s chairman, who led the connectivity assessment, said the study had concluded that both projects were possible.

“However, a bridge crossing would be the longest span built to date,” he wrote. “A tunnel would be the longest submarine tunnel ever built, given the limited gradients trains can travel on, the route they must take, and the depths they must reach.”

Building a rail link would also create “some complexity”, as 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 was an “excellent question to ask”.

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

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

Ideas in the broader connectivity review included investment in the west coast rail line north of Crewe to provide better connections to Scotland, beyond the £96bn rail plan announced last week, and an upgrade from the A75 road, which runs from the M6 ​​at Gretna Green to the Scottish ferry terminal Stranraer.

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