If you should ever find yourself wondering what the European Union is really about, take a drive from Rennes, in Brittany, to the Spanish city of San Sebastián.

The autoroutes are stuffed with trucks heading from St Petersburg to Porto, from Malmo to Murcia and from Bratislava to Bilbao. In addition, tens of thousands of HGVs each day shuttle between France and Spain. When, for any reason, the road is blocked, the buildup of lorries can extend back several miles.

All my wife and I wanted to do was ‘nip’ down to Spain for a few days in the sun. Instead, constant vigilance was required over a nightmare drive of some 800 miles. Just passing a convoy of trucks took five minutes at a time, at speeds in excess of 70mph. Occasionally, two truck drivers would enter a duel, thundering along in parallel while a snaking line of cars followed in their wake.

Relaxing is not the word that comes to mind.

But it makes you realise that Europe has become a densely interconnected place. Every city every day receives hundreds, if not thousands, of deliveries from other parts of the EU. At the same time, every city every day sends out massive consignments of goods bound for destinations five hundred, one thousand, even two thousand miles away.

The EU may bleat on about its constitution and the urgent need for reform of the decision-making process in Brussels. But take it from me, it is the constant circulation of heavy goods vehicles that ultimately makes sense of the enterprise.

I was surprised as we drove along in our little Ford Ka that I didn’t see a single Irish lorry, and not too many from the UK. But there were hundreds each from Poland, Portugal, Slovakia, Estonia, even Russia, as well, quite literally, as thousands from Germany, Belgium, Italy, the Netherlands, France and Spain.

Without these trucks, the economy of Europe would grind to a halt. There would, in fact, be no economy. Yet, undeniably, the arterial network is clogging up. Existing roads can barely stand the strain. New ones are needed all the time. But the doomsayers aren’t wrong. The problem is not simply that we cannot keep on and on building roads, it is also the fact that the planet is rapidly running out of oil.

It cost me €175 to get from Brittany to San Sebastián and back in my 1.3 litre Ka. I have no idea how many gallons, or litres, of diesel a 44-tonne truck uses per mile of motorway. But from Warsaw to Madrid is a journey of some 1,500 miles. The cost in fuel alone has to be at least €1,000.

Given the sheer volume of trucks on just this one route, it is safe to say that millions of gallons of diesel are used every week between Rennes and Irun.

But there are a dozen such routes in France alone, plus similar networks in every other European country. The amount of oil being exhausted is breathtaking.

Currently, there are more than five million HGVs in the EU. That’s enough, I reckon, to form a convoy 30,000 miles-long. It’s insane. Something has got to be done before the oil runs out or the carbon emissions turn us all into mutants. But, as they say in New York, waddyagonnado? Everybody knows that there are too many commercial aircraft in the the skies. Everybody knows that we can’t go on the way we are. Yet was there joy, or was there not, when Bombardier announced last week that it would invest £500m in its east Belfast plant?

No one thought to ask, what are we doing adding more aircraft to an already congested sky? All we thought was, jobs for us — brilliant! Like the man said, why should we care about posterity, for what did posterity ever do for us?

As I struggled to survive the Bordeaux giratory system, flanked by lorries as big as houses, I couldn’t help wondering what Europe will be like when the oil does finally run out. The motorways will slowly revert to nature.

The trucks themselves will rust away. And our grandchildren (representing posterity) will ask themselves why their grandparents couldn’t see the bleeding obvious.

San Sebastián, by the way, was great. I know that the locals call it Donostia and that it is, properly, a Basque city, not Spanish at all. But it seemed pretty Spanish to me. There were bars everywhere, serving beer and tapas. Shops closed at one-thirty and didn’t re-open until half-past four. Dinner began at 10pm and continued until one in the morning.

Fabulous! But how are we going to get there in the future when the oil runs out? Is it going to end up like it used to be, with people living their entire lives within 20 miles of where they were born and reared? Dear God, am I seriously going to have to spend my last days in Millisle?