[Diesel_Dave]

As someone who works as an engineer in diesel R&D, these types of governement mandates & regulations make me want to pull my hair out sometimes.

First off, the heavy-duty truck market (e.g., semi trucks) has pretty much always been the engine application that has natuarally put the highest emphasis on fuel economy. The free-market has naturally driven this. Heavy-duty truck buyers are willing to pay for fuel economy. It's simple to see why. If you do the math you can see that a 1% improvement in FE saves a truck owner almost $1,000/yr. Compare that to the average pickup owner who's hard-pressed to even notice a 10% improvement.

Very few people also know how much improvement has happened on it's own as well. I can't find the exact figures right now, but a while back I remember seeing a chart of average FE (in gal/ton-mile) of heavy-duty truck over the last 50 years or so. If I remember correctly, I think FE has nearly doubled since 1970. All this without regulation. Why? Because the market will pay for FE.

Trucks and engines can be made to get substantially higher FE today. But it's always a matter of cost. We can add additional technology to an engine (like more advanced fuel systems, more advanced turbos, etc.) that will improve FE, but if the increased cost is so much that it won't pay for itself, then the customer won't pay for it.

If you set a standard in a regulation one of two things will happen.

Here's the first scenario:
The standard is lower than what the industry would do on it's own. In this case, the standard was unnecessary, and cost the industry millions in extra money testing the trucks & engines to show the government that they met the standard.

Here's the second scenario:
The standard is higher than what the industry would do on it's own. In this case the government has forced to customer to pay for more FE than will pay for itself. For example, the customer will have to pay $15k more for a truck that gets 1% better FE (a 15+ year payback). Oh, and there's still the extra costs to the manufacturers for all the additional testing to prove they met the standards.

It just doesn't make sense to me.