And, to our admittedly untrained ears, the cost, estimated at between £4 billion and £6 billion, sounds optimistic, given the Edinburgh tram line from the airport to the city centre ended up costing more than £1 billion.
But, if Boris Johnson can trumpet the idea of a bridge linking Scotland and Northern Ireland, who can begrudge a display of ambition from the Scottish Greens? The party is proposing a slew of major rail projects – also including full electrification by 2030 – totalling some £22 billion.
Many, including the Scotsman, have suggested that “Boris’s Bridge” is a non-starter and it probably is unlikely that the tunnel will ever get under the ground.
However, it is a mistake to simply dismiss ideas out of hand because they seem too big, too expensive or too bold.
The Channel Tunnel had been talked about for two centuries before it became one of the greatest achievements of the Conservative governments of the 1980s and 1990s. And it remains a shining example of what we can achieve when we put our minds to it.
So, who knows, perhaps decades from now people will be celebrating the vision of those who built a seemingly unbuildable bridge and dug a most wonderful tunnel.
We just need to make sure we learn the lessons of the tram fiasco – with the help of the long-awaited findings of the inquiry into what exactly went wrong – and avoid the condemnation of future generations for our folly and overweening ambition.