Fact: Cost and reliability on a per mile basis has never been lower, with very successful and well tested Tier 3 technologies adopted in '08.

Yes, Tier 4 is very difficult, and I thought and recommended at the time, more time before the Tier 4 mandates, and because the benefits at a low cost from more Tier 3 replacement due to high fleet turnover is doable, and gives very substantial benefits.

I agree that Tier 4 is a real stretch with dirty diesel fuel, due to the after treatment issues, and a lack of technology readiness, which may not be doable at a lower cost per mile, like the Tier 3 engines.

And, yes, Doctor, there's going to be a fair amount of the usual trolling and misinformation on this one. But, on this one, the jury is still out, and the standards may actually be counterproductive, as I actually see a lot more benefits (reduced actual emissions) from continuing Tier 3 replacement of the existing fleet, than in pushing this difficult to achieve standard, prematurely.