It reads:

It is perhaps a sign of the times that political stories, which wouldn’t even have seen the light of day in the past, gain traction.

The latest is the proposal of a bridge (although we’re told that was a metaphor, and it may now be a tunnel that’s being proposed) to link Scotland and Northern Ireland.

This is the idea – and this is not an April Fool – to consider a 21-mile road link between Scotland and Northern Ireland over the Irish Sea.

Somewhere, engineers will be debating the technical challenges of building a bridge over deep water, or a tunnel across a difficult underwater terrain. Geographers will be working out the average windspeeds that traffic will be able to withstand. And munition experts will be discussing how to avoid Beaufort’s Dyke.

But before this gets any further, hopefully the government will ask their civil service economists for some advice.

What will they say?

Firstly, those hoping that building a bridge (tunnel or giant catapult even) will automatically be a catalyst for faster economic growth in both Scotland and Northern Ireland will be sorely disappointed. Many infrastructure projects displace existing activity from elsewhere and create deadweight. In fact, there is little international evidence to suggest that there is always a causal positive link between infrastructure and growth. Build it and they will come, is sadly not the case. See our recent report for the Infrastructure Commission or a really accessible report by Iain Docherty (Stirling) & David Waite (Glasgow) for the ESRC’s Productivity Insights Network.

Secondly, and that being said, well-designed and targeted investment that helps to unblock barriers to connectivity, can have an impact on growth. But on a list of top 10 infrastructure priorities in Scotland (and the UK), this won’t be one of them. Much higher priorities concern improving how people move around our cities – e.g. see the work of the Glasgow Connectivity Commission – in an efficient and joined-up way; better linking-up our major centres of economic activity (it still takes 2 ½ hours to travel between Aberdeen and Glasgow); sorting out major infrastructure weaknesses (such as the Rest-and-be-Thankful) and providing sustainable solutions for many rural communities that remain poorly served by public transport.

Thirdly, the proposed bridge or tunnel won’t actually link up centres of economic activity. Instead, travellers will arrive in rural Dumfries and Galloway or Argyll, with a 90+ mile drive to the central belt (at least a further 2 ½ hours). This won’t improve connectively to the point where any hope of clustering or agglomeration economic effects could be expected to take hold.

Fourthly, you may have noticed that we have a target to transition to net zero by 2045. The consistency of building infrastructure which has, at its heart, people driving long distances doesn’t stack-up. And this is even before the enormous emissions costs required to build a tunnel or bridge with thousands of tons of steel and concrete are considered.

Finally, and one of the first things that economists are taught is to look at the ‘opportunity cost’ of a project. The opportunity cost isn’t the financial cost of building the bridge (estimated at least at £20bn), but the benefits that could be gained instead from spending that ~£20bn on other projects in Scotland (and Northern Ireland). £20bn would be equivalent to over 14 Queensferry Crossings (with some change left over to fix the problems of ice); 25 M74 extension equivalent road projects; or 400 large Cal Mac ferries (at the original price). £20bn could be far better spent.

So in short. It won’t deliver the economic boost some claim, it isn’t a priority, it would go to the wrong location, it wouldn’t be consistent with climate change objectives, and the money could be better spent on other things.

Apart from that, it’s a cracking idea.