Irish Sea fixed crossing

Proposals for fixed sea links to improve transportation between areas of the British Isles include undersea tunnel, bridge, causeway, or combination of these elements.

This is the shortest route at around 19 km (12 mi), from the Mull of Kintyre to County Antrim.

This route has been proposed as either a tunnel or a bridge, However, because of the Beaufort's Dyke sea trench, this route would be deeper than the southern routes. It is believed that such a project was considered by railway engineer Luke Livingston Macassey in the 1890s as "a rail link using either a tunnel, a submerged "tubular bridge" or a solid causeway".

This route (from Dublin to Holyhead in Anglesey, Wales) would be about 100 km (62 mi) long.

The Institute of Engineers of Ireland's 2004 Vision of Transport in Ireland in 2050 imagines a tunnel to be built between the ports of Fishguard and Rosslare along with a new container port on the Shannon Estuary, linking a freight line to Europe. This report also includes ideas for a Belfast-Dublin-Cork high-speed train, and for a new freight line from Rosslare to Shannon. This route would be approximately twice the distance of the English Channel Tunnel at over 100 km (roughly 60 miles long).

A 1799 description of a failed proposal for a bridge from Howth to Holyhead is a mocking metaphor for the failure of the Union Bill 1799, which succeeded next year as the Act of Union 1800.

Between 1886 and 1900, proposals for a link to Scotland were "seriously explored by engineers, industrialists, and Unionist politicians". In 1885, Irish Builder and Engineer said a tunnel under the Irish Sea had been discussed "for some time back". In 1890, engineer Luke Livingston Macassey outlined a Stranraer–Belfast link by tunnel, submerged "tubular bridge", or solid causeway. In 1897 a British firm applied for £15,000 towards the cost of carrying out borings and soundings in the North Channel to see if a tunnel between Ireland and Scotland was viable. The link would have been of immense commercial benefit, was significant strategically and would have meant faster transatlantic travel from Britain, via Galway and other Irish ports. When Hugh Arnold-Foster asked in the Commons in 1897 about a North Channel tunnel, Arthur Balfour said "the financial aspects ... are not of a very promising character".

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