can't even guess at the physics, but perhaps there's something other than wind drag involved?  For example, maybe the air/fuel ratio is better or something at 70 than 55, or maybe the 187,000 mi catalytic converter is doing weird things.  I really, don't know, but, UM, the fact that I need to fill up the tank less seems to give credence to the improved mileage my car claims to have since I've started experimenting.

How much energy does the manufacture and transport of a new Prius use vs the extra gas I'm using at an average 27.4 MPG instead of 50ish that a Prius might provide (I live in the mountains and word has it that hybrids don't do as well here, so perhaps 45 is closer)?  This isn't snark, it's a serious question.

What's the energy use break-even point if I cause the manufacture of a whole new car instead of using the car I already have more efficiently?  If I'm even going to consider shelling out mucho dinero for a new car, I need to know whether that switch is actually going to do what it's supposed to do.