What do we make of this? First, what we know as fact.

Cummins has decided that, as a result of a combination of higher fuel prices and advances in catalyst technology, SCR is now the way to go for its heavy engine range post 2010. The press release is here.

This is fair enough, and so a market that had offered two different routes to compliance now offers SCR and the as yet unproven Navistar engine.

Who wins? Daimler and Volvo without a shadow of a doubt. Both have 13 and 15-ish litre engines on the blocks, all using SCR, and now with no obvious differentiated technology against which they must compete. Whilst the US market seems likely to adopt 13 litre engines at some point, 15 litres still seems the place to be, and with a bit of price and warranty competitiveness, we see few reasons to suspect that both DTNA and VTNA buyers will eschew the home-grown in favour of the outsourced.

Paccar is a bit of a mystery here. The MX engine will arrive in 13 litre guise alone, and so Cummins is the obvious choice as a 15 litre option. We expect it to do some business here, at least initially.

Navistar is a vey difficult one to call. With two engine manufacturers offering EGR, there was some legitimacy attached to the claim that it provided an alternative at EPA 10. Only one manufacturer doing thus does much to reduce that. Cummins argues that, whereas its EGR EPA 10 unit could reasonably have been expected to perform on a par - in terms of fuel efficiency - with its 2007-compliant engines, adding SCR will improve that same figure by five per cent. We await Navistar's claims with some interest, especially in the light of that which we have heard from MAN in the past.

As for Cummins, what had looked to be a very bright future at the heavy end of the North American truck market now looks to be rather less so. It gets to compete with three manufacturers, all with global engine platforms, all with volume and scale firmly in their sights, and all with something of a point to prove. That's not a fight that we'd be looking forward to one bit.

On the plus side, Cummins' adoption of SCR should do much to boost the development of a DEF (aka AdBlue) infrastructure within the US. On the downside, urea costs have almost doubled this year.

And what of the pre-buy impact? This does change things rather; if Navistar remains wedded to EGR, then it is the only non-SCR supplier post 2009. If we take the conclusions arrived at by UBS a while back - namely that 81 per cent of the operators polled in its 13^th Quarterly Truck Survey were opposed to SCR, then we have to assume that there will be at least some reflection of this disdain moving through 2009. Does the US market need a pre-buy spike? It could certainly do with some truck buyers, but a headlong rush to avoid an unproven technology would not be welcome.

In some ways, it's easy to understand why Cummins has done what it has done here; however, we would have thought that, with its EGR solution supposedly ready for launch in 2010, it would have opted for a twin track approach, and offered both SCR and EGR, at least initially. As it is, this volte face is far from adroit, and leaves Cummins without much by way of ammunition to compete in a market that is becoming ever more verticalised.