Alternative could link Glasgow to Northern Ireland, says expert

The £20 billion connection between Northern Ireland and Scotland that was backed by Boris Johnson earlier this week could become a chain of three floating bridges using the Isle of Arran as a stepping stone to link Glasgow directly with Ulster or even a tunnel submerged twenty metres below the surface of the Irish Sea, according to experts.

Alan Dunlop, the architect who first proposed a Scotland-Northern Ireland road bridge in January 2018, said the shorter of the two routes he had analysed, crossing the 12 miles between Torr Head and the Mull of Kintyre, would be a viable option if two additional spans connecting Kintyre with Arran and the mainland were built, slashing the five-hour journey on narrow roads between Scotland’s largest city and the tip of the peninsular.

He calculated that the total cost of this route would be in the region of £20bn to £24bn, based on a study of previous sea-bridges, including the £4bn Ǿresund Bridge between Copenhagen and Malmö that opened in 2000. On its own, a bridge across the narrowest point of the Irish Sea would cost £12bn.

The alternative, a 26-mile crossing from Portpatrick to Larne, would cost between £15bn and £20bn, but would still be shorter than the Hong Kong-Zhuhai-Macau bridge, which has about 30 miles of its span over water and is designed to cope with typhoons. However, it would involve crossing the 300m-deep Beaufort’s Dyke, a vast submarine trench where over a million tonnes of munitions was jettisoned after the second world war, alongside two tons of radioactive waste in the 1950s.

“I’m as confident as I can be that you can make the structures for that price,” Dunlop said. “Compared to HS2 [the railway line that could cost up to £106bn] it seems quite reasonable so maybe the government doesn’t want to investigate too much!

“Of course, we’d need to find out exactly what’s in the dyke, as the estimate seems to grow every day, even though most of it seems to be to the south and we could cross the north of the trench. But no matter what the challenges are, we have the talent in the UK to tackle them.”

Harbiner Singh Birdi, an infrastructure expert at Hawkins/Brown who has worked on Crossrail, agreed: “Any engineering firm worth their salt will be chomping at the bit,” he said. “But while we can price concrete and steel, there are a lot of unknowns that could prove expensive. And then there’s the cost of maintenance.”

Whilst his initial design featured enormous towers stretching down to the seabed and a deck hung from cables, Dunlop believes any future bridge is more likely to utilise floating platforms tethered in place, pointing to the enormous hurricane-proof oil platforms in the Gulf of Mexico, held fast by 5000m cables, and the £36bn Norwegian Coastal Highway, which crosses fjords 500m deep using spans supported by floating pontoons.

Norway’s largest ever infrastructure project may also come to make use of a new generation of moored underwater tunnels, a solution favoured by Ian Firth, a structural engineer with 39 years’ experience of constructing bridges. He believes the risk of a large ship crashing into a pier is significant enough to justify submerging the route in a giant tube 20m down - after all, that was one reason the Channel Tunnel was chosen instead of a bridge to France (an idea previously embraced by the Prime Minister) – although he also questioned whether the crossing was in the right place, suggesting a connection between Dublin and Liverpool, in shallower seas where artificial islands could be created, might be a better option.

“Deep water is one of the big challenges of all but the idea of tunnels anchored 20m beneath the waves is interesting to explore and might even be cheaper,” he said. “What needs to happen now is a proper feasibility study by people with the right skills.”

Yet for all the engineering complexity, the biggest obstacle may be political. Despite conducting the first study (on behalf of a newspaper) Dunlop said he has yet to be approached by anyone from central government but admitted the vitriolic response from Johnson-hating nationalist politicians worried him, with Nicola Sturgeon, Scotland’s First Minister, declaring this week that the money “could be spent on more important priorities.”

However Peter Griffiths, Cities Strategist at ING Media, cited the example of HS2: “Quite a few successive governments had to be supportive to get it through and it probably won’t be Boris that gets to build this crossing. We’ve been talking about a bridge across the Irish Sea since 1897, when it was first suggested by an MP, and we’ll probably still be talking about it in five decades’ time.”