To what extent it's going to plumb the depth is a different matter. Think of a number between 1 and 100, apply a minus sign to the left, and a percentage mark to the right, and you, my boy, a truck industry pundit have become. Just about anyone in the US who can differentiate between a truck and a tangerine has an opinion, and those same opinions cover just about every numeric possibility.

So let's call things to order a bit, average out the most recent set of numbers - culled mainly from the recent Mid America Truck Show - and establish a third-of-a-year figure.

The Tier 1 manufacturers are not happy. We've spoken to three of them, and they predict a US Downturn of 37, 48 and 75 per cent respectively. The OEMs - and we've garnered the opinions of five US manufacturers - see the market dipping by 35, 35, 38, 36 and 40 per cent respectively. This gives us an averaged out figure of a 43 per cent drop, and suggests a likely Class 8 market size for 2007 of 182,400 units, down from 320,000 in 2006. This sounds unpleasant, and yet is reflected in capacity cuts now being made by the US based OEMs: Kenworth has just announced a shutdown of its Renton, Washington plant, followed by a 40 per cent cut in output.

Should this impact upon Europe - the second of the Triad Markets? It's some distance from the EU to the US, and, taken as a whole, the European market is holding up rather well at present. Figures for February show that new heavy truck registrations in Europe (EU22+EFTA) went up by 11.7 per cent, reaching 21,856 units. The increase was much higher in the new Member States - at 77.2 per cent - but, even so, the old pre-accession EU15 states still saw a 4.4 per cent increase in registrations.

The last time the US truck market went over the edge of the cliff was during 2001. But five years ago, things were different. Europe could watch the machinations of the US market with little more than an indulgent interest. True, European OEMs did own a majority stake of the US truck business six years ago, but, six years later, that which they still own a large chunk of has changed shape quite markedly. And those changes across the Atlantic mean that the US and the European market are now more closely linked than ever before. Put simply, what hurts in the US is likely to cause some concern in the EU.

The reasons for this transatlantic pessimism are two-fold. On the one hand, shares in US truck manufacturers and Tier 1 suppliers are all listed on the US exchanges, and those stocks in the same are rated by investment analysts, and a view taken as to their respective value and risk. Such ratings tend to be short term - and are based around the quarterly report. A quarterly report that shows double-digit decreases gets the attention.

And as US OEM and Tier 1 shares are downgraded - as has happened recently with Volvo, for example, then so a perception of risk increases. As more automotive stocks come under the spotlight, then so, inevitably, will borrowing costs for those same companies rise. In other words, it becomes more expensive to be a truck manufacturer. Are they all coming under the spotlight? "Yes," says Ann Duignan at Bear Stearns. "There is very little interest in the marketplace for 2007 trucks as the large fleets are holding out for a weaker environment in order to negotiate better prices going into 2008 and 2009," she wrote in a recent research note.

But isn't that a US problem? In part yes, but there's another far more significant raft of expense that has to be shouldered. With the exception of Navistar - owner of the International brand - all of the US OEMs are linked to Europe by ownership. Despite the fact that most of the brands function as separate companies at many levels, the fact remains that, ultimately, there is but one pot of money.

The US has always been a cyclical, volatile truck market. No change here; but in the past, the impact of its cyclical volatility was mitigated by a spread of risk across a group of Tier 1 suppliers. Traditional US truck manufacture saw the OEMs assembling trucks. Components were almost all sourced from the Tier 1s, and so, during a downturn, those same Tier 1's found themselves holding the bag. This has now changed, and it is the OEMs - and their shareholders - who are left counting the cost.

There is far more verticalisation within the US business today. Volvo, for example, supplies 65 per cent of its North American output with eponymous engines. PACCAR is planning to do likewise with its MX engine, due on stream for EPA 10, and we've already spoken at some length about DCX's plans for HDEP. As an aside, whither CAT in all of this.

This is splendid during the good times - the verticalised OEMs gets a far bigger piece of the pie - but during the bad times - they have to retrench. And retrenching isn't cheap; capacity has to be paid for.

And that payment comes out of the same large - global - pot of money already alluded to. As revenues plummet in the US, so any OEM with a US relationship - Mercedes-Benz, Volvo, Renault and DAF - will almost inevitably find itself working overtime to help stem the tide. If there's less money to go around, there's less money to go around everyone.

Does this mean that - in the light of the seemingly fairly robust European truck market - that prices will firm up a bit? Europe is already a price-elastic market, and so, in the short term, this seems unlikely.

But, just around the corner comes EPA 10, and the whole US market cycle kicks off once again. Many US fleets have delayed replacement programmes at the onset of 2007, but demand is likely to creep up again next year - assuming the US economy retains at least some vestige of robustness. Capacity will have to match this demand, and again, a cost will be incurred. Then EPA 10 bites, and, once again, the waves of woe start to lap against European shores. Can the US OEMs go from flat out to nothing to balls back against the wall in the space of 36 months? Not without a very fair following breeze, we would posit.

This is the Magic Roundabout for the globalised age. Ultimately, boom-bust cycles in a single global industry will have to be seen as unsustainable. But they will remain with us for a while yet. It is perhaps rather ironic that the very thing that the auto industry has pursued relentlessly over the past few years - scale borne out of a global presence - is the very thing that - in truck terms - stands to do it huge damage.