Few infrastructure proposals have polarised opinion as much as the 'Boris Bridge', and now the 'Boris Burrow'.
Initially envisaged as a bridge to Scotland, at an estimated cost of £15-20bn, the severe Irish Sea weather typical has now turned minds to a tunnel.
There is no doubt that such a link would have benefits for both Ireland and Scotland, allowing freight to move more easily and reliably between the two islands.
I do not share the pessimism of those who believe it to be impossible. The technology exists to solve the significant problems likely to be encountered.
A 300-metre-deep underwater trench filled with disused munitions is perhaps the most obvious, but there also the questions of where the approach tunnels would reach the surface, the fact that the two islands operate different railway gauges and the recently-created requirement for customs checks on traffic using it.
Nevertheless, a feasibility study is likely to show that it is practical.
Feasibility alone, however, is not enough to justify spending these levels of public money on infrastructure. It must also be cost-effective.
It is highly unlikely that the economic benefits of such a link would exceed the cost of building it within a reasonable timeframe. With a population of just under seven million, there are simply not enough people in Ireland to provide the level of commerce needed to justify it.
The Channel Tunnel, by contrast, links Great Britain, with a population of 60m, to continental Europe, home to hundreds of millions more. Perhaps the bridge will be justifiable by the latter end of the 21st century, but not today.
The purpose of the tunnel seems to be to foster closer trade links between Northern Ireland and Great Britain. If this is the objective, there are better ways of doing so.
An entirely free car ferry service between Northern Ireland and Cairnryan, for example, could be set up in months, be subsidised for decades, and still cost less money.
Of course, it is not clear where the money would come from, except that such a huge sum could not come from Stormont.
But if the aim is economic benefit, there are many competing infrastructure proposals that would bring more immediate benefits at a lower cost.
For example, expanding the rail network into the west and adding stations for our struggling airports.
On the road network, £20bn would be enough to dual all five of our key transport corridors (basically, the A4, A5, A6, A26 and A37) with change to spare.
Dualling the entire A5, for example, would cost a comparatively paltry £1.2bn.
Even York Street Interchange in Belfast, which would greatly benefit commerce, would cost less than 1% of the cost of the Scottish link at £130m.
On the Scottish side of the water, dualling the A75 and A77 would bring real benefits to Northern Ireland too.
We will always welcome investment in Northern Ireland, but if money is there, there are better ways to spend it than on a tunnel.
Wesley Johnston is a leading commentator on the Northern Ireland road network. His website is www.wesleyjohnston.com