Walking for dollars

Gas hit $3.60 a gallon in my neck of the woods this week. I keep thinking I'll see the pedestrian revolution: people leaving their cars at home, taking the bus, walking to the store. Perhaps we are the legendary frog in the kettle who never realizes that the temperature of the water he's in is rising - until he's cooked. Would we jump out of our car kettles if the price soared from the 77 cents I paid around 10 years ago to its current price?
Maybe nobody has crunched the numbers for us, so here, briefly, is how the cost of driving looks to me. Currently, our family vehicles get around 20 mpg, so 20 miles costs $3.60 or 18 cents per mile. If I'm lucky, these cars we bought used will generate 100,000 miles each for their average purchase price of $11,000 (including interest). That yields an ownership cost of 11 cents per mile. Insurance on such old cars isn't much, and doesn't change regardless of how many miles we drive, but it isn't completely unrelated: if we drive less, the cars last longer and our insurance premiums drop. So I factor in 24,000 miles per year divided by $720 per year, and get 3 cents per mile. Older cars are racking up "used car payments" at the shop, so I figure maintenance and repairs at $1440 per year over the same miles and add another 6 cents per mile. I'm up to 38 cents per mile.
Your results, as they say, will differ. You may surmise that I am "frugal", and you would be wrong. I am cheap. Had I bought a new car, the ownership and insurance costs would have easily pushed the total over the federal mileage allowance of 48.5 cents per mile.
These are the direct costs to me, and I would argue that, if I drive when I could walk, the costs are even higher: short trips burn more fuel and are harder on engines than long ones. There are other costs which are real, but it's hard to say who is going to be asked to foot (forgive the pun) the bill: the costs you will pay down the road (forgive the pun) for your health care because you chose not to walk or bike; the costs (and who knows when these will come due) to clean the environment; the costs to pay for police, and insurance claims, in neighborhoods where no one is moving slow enough to notice the difference between normal and abnormal activity; the infrastructure costs of building and maintaining roads. There is also a growing body of research that suggests that not knowing your neighbors comes with a steep price in emotional health - which in turn affects my health, productivity and conduct in society. And you might also be saving the cost of your health club membership. Finally, since fuel is largely imported, driving increases our trade imbalance and generates more debt.
When I have the choice to walk, walking saves me and all of us money.