[Spacemonkey1023]

Well, correct me if I'm wrong, but isn't the amount of exhaust produced more a product of engine effort than speed? If that's the case, then wouldn't it be better to go fast and keep the engine at low RPM than going slow and having to accelerate/decelerate constantly?

[doc1019]

Couldn’t they just buy some “carbon” credits from Gore’s outfit and put the pedal to the metal?

[ProtectOurFreedom]

The power required to push your car through the air is proportional to drag. Drag depends on the "drag coefficient" C_D, densitiy of the fluid, velocity squared and frontal area S. If you double your speed, you require four times the energy to go through the air. Sure you'll get their in half the time, but the quadratic term dominates. Maybe your engine's efficiency will be 10% or 15% better at one speed or another, but that will be totally dominated by the velocity squared term.