A Wales to Ireland tunnel could prove to be a "more attractive" prospect than the previously suggested Scotland to Northern Ireland link, according to tunnelling expert Bill Grose.
Last week transport secretary Grant Shapps suggested an 80km tunnel to connect Ireland and Wales in an interview with the Financial Times, with reports suggesting the route could run from Holyhead to Dublin.
Tunnelling consultant Bill Grose - a former British Tunnelling Society chair - told NCEt hat the existing infrastructure in Holyhead and Dublin could make the route a better option than the previously mooted link from Belfast to Stranraer.
"I can see it being more attractive to investors because you’re connecting more existing infrastructure on the Welsh side with more on the Irish side," he said. "Dublin is bigger city than Belfast. There is more infrastructure in Holyhead than Stranraer. It’s less of a business risk."
Given the existing road and rail infrastructure in place in Holyhead and Dublin, Grose said he suspects "the additional landside infrastructure costs would be less".
He added that Liverpool and Manchester are closer to Holyhead than to Scotland so if trade and passenger routes between Britain and Ireland were mapped out, a Wales to Ireland connection "would make more sense from a transport point of view".
Water depth is another key element, with the Irish Sea between Dublin and Holyhead relatively shallow - 120m at its deepest.
Grose explained: "The water is not particularly deep so it would be possible to build an island or put some sort of platform or cofferdam halfway across, either temporary or permanent, to provide some sort of ventilation or access. So I think the water depth helps. It makes it quite attractive in tunnelling terms."
According to Grose, the tunnelling costs would be likely to be in the region of £5bn to £7.5bn with a project cost of £15bn a reasonable first estimate.
It is unclear whether the proposal favours a road or rail tunnel but Grose backed rail as a more realistic option, since technology for long distance rail tunnel travel is more developed than for road tunnels. The tunnel would be almost twice as long as the 50km Channel Tunnel.
Various options have been put forward for a Scotland to Northern Ireland crossing since the bridge option was first suggested.
Downing Street officials have recently suggested that three tunnels under the Irish Sea could connect in an “underground roundabout” beneath the Isle of Man. The proposal includes three starting points: at Stranraer, Heysham, near Lancaster, and one near Liverpool. Then a single tunnel would run on from the Isle of Man to Northern Ireland.
Grose has previously highlighted several challenges presented by the proposal. He added that another strength of the Wales to Ireland suggestion is that it would be "shorter in total tunnelling terms" than the Isle of Man route.
"[Going from Holyhead to Dublin] is about the same distance as Liverpool to the Isle of Man," he said. "So in total terms it’s a good crossing. Building Holyhead to Dublin would be like connecting England with the Isle of Man but the advantage is you get across to the island of Ireland but going to the Isle of Man you’re only half way there."
Formal proposals for an Irish Sea link between Scotland and Northern Ireland have been put forward by various groups as part of the government's ongoing Union Connectivity Review which will look at how to boost transport infrastructure throughout Scotland, Wales, Northern Ireland and England via road, rail and air, and across the Irish Sea.
The review will be published in the summer. Its interim report concluded that further work should now be undertaken to look at a "fixed link" across the Irish Sea.