"For a family driving a modest amount, say 15,000 miles a year on two cars, and driving vehicles that do well on overall fuel economy, say 30 mpg, their annual fuel costs would be $10,000."
This 15K a year has shown up both earlier in the book as an expectable amount of driving for brand-new-car owners in India and China, and it has shown up earlier in my blog as apparently what some people think of as a typical amount of driving to do in the course of the year. Now me (and remember, I've driven 1200 miles in a day. More than once), I think that's wholly unreasonable. I think 12K is a more reasonable number, and the one I recollect from my younger days. We put less than 12K/year on our two vehicles. Combined. But wait! He doesn't mean 15K combined! He means 15K _each_! OMG!
Well, you know. Sell one car, replace it with a really decent mileage vehicle that you preferentially drive, cut your mileage as much as you can (walk, bike, public transit, eliminate trips, order online, carpool, vanpool, work 4 tens, you know what everyone did when we hit $4, right?). If you can, sell one car and don't replace it -- the savings on insurance, taxes, maintenance etc. will help _a lot_.
If people did all that stuff at $4, why would he be treating 15K/yr driving as normal ongoing behavior at $10? I _just do not get it_.