Funny how people moan about the price of petrol, but do little about it. Why is that?
I can think of two good reasons. First, for many, their car is an important part of their self-image. Yes, I find that hard to believe too, but I've found it's true. Otherwise quite intelligent people agonize for months over exactly what car they should buy next not on the grounds of whether it's efficient, or can carry their kids, or whether it'll fit in the garage, but on the basis of what their colleagues, girlfriends, golf club buddies etc. will think of them when they arrive somewhere in it.
And conspicuous consumption of fuel is equated with status. So people charge around in ridiculous "lifestyle" 4WDs. (Odd that the same people will also moan down the pub about the price of fuel, but there you go. They probably also drove to the pub to do it...)
The other reason: you drive your car around six days a week (say) and it doesn't cost you a penny! It's only the one day a week when you take it to the petrol station that you have to hand over a wad of notes to fill the tank. This is irksome, but it probably doesn't cross your mind when you start the thing up to drive it 500 yards to buy a paper, or ferry the kids half a mile to school or whatever.
If cars had a coin slot on the dash like old-fashioned electricity meters, and you had to shell out real, physical money every time you drove it, it'd make people think a bit harder about whether it's really appropriate to use a car for each journey.
(Is it too late to patent this idea now?...)