What I was obliquely alluding to is that the general population does not think in terms of physics text books.

They are merely interested in "bang for their buck" and they define "bang" as vehicle capacity and power. Hence the love of large SUV's in the USA.

Sure, *in principle* you could mandate fuel economy. It's been done before - remember the 55 mph speed limit?.

Unfortunately for the world, unless there is a very strong reason - like an energy embargo - it is political suicide to mandate vehicle economy in the land of the brave and the free.

Leave that to the Eurosocialists, who drive pissy small cars anyway.

Who cares if the USA and China get in a bidding war for the world's oil supply capacity? It suits me down to the ground. (My income rises at about the square of the price of oil but my expenses rise as about the square root.)

Expensive oil is good*, SUV's are good*, Greenhouse gasses are good*, conspicuous consumption is good.*

* Provided that you define good in a narrow, greedy, crass commercial way. But since this is the way the world is going, if go to Hell**, I'll have lots of company!

** I may not need to make the journey. The way the world is going, life here will be Hell!

The USA better keep spending big on defence before there is world war over oil with China, or a world war over obscene consumption with the rest of the world!