in itself it wouldn't even facilitate movement of traffic.
Just look at a map. The two routes that have been mentioned - (1) the shorter crossing of Portpatrick, near Stranraer in southwest Scotland, to Larne in Northern Ireland, or (2) the longer crossing of "somewhere" on the south end of the Kintyre Peninsula to "somewhere" on the Antrim coast (presumably near Ballycastle) - would funnel traffic on the Scottish side onto roads poorly suited to increased traffic flow with limited scope for improvement, (1) leading on to the A77 north (of limited use for access to the rest of the UK) or the A75 east to Gretna Green (Ever travelled that part of the M74/M6? - It can already be nightmarish), and (2) leading on to the coastal A83 in an area of Scotland that even we who live here consider pretty remote, and involving a very long trek northward then northwest on already cluttered A roads, some liable to landslides and closure in poor weather, before the existing network gets you anywhere you can strike south towards the central belt.
I'm not familiar with the roads on the Northern Irish end, but I imagine the same applies. A new rail link on the Scottish side might help with route (1), but that would be a very major undertaking and would go against all trends in transport thinking. No such option is possible for route (2), the most "sensible" option there being ferries to take traffic exiting the bridge closer to the main road network!
The estimated cost of £15 billion for just the bridge itself is likely to escalate alarmingly given experiences with major projects like the Channel Tunnel and HS2 (the Scottish Government did manage to bring in the new Forth crossing in on budget and on time, but that's enough of a rarity in such projects that it was cause for major celebration).
Does the likely future traffic flow even justify such an undertaking? More capacious and robust ferry links would serve the same purpose with far fewer complications (though still subject to the same problems with traffic flow at either end).
Sea routes have historically been the transport mode of choice in these coastal areas of Scotland since historic times - for good reason!
The idea has met a mixed reception in Scotland so far. Some look at ambitious infrastructure projects like those in Denmark/Sweden, Norway and the Faroes (which has extensive links between its islands, both bridges and tunnels) and don't dismiss it out of hand, but the scale of what's been suggested with either route and the nature of the seas, undersea terrain and prevailing weather mean this is a whole different ball game.
Still, with Grayling's name, expertise and track record associated with it, I'm sure I'll have to eat my words in the fulness of time.
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