It really doesn't, though, especially if you've already decide to drive 10 or 20 miles for some other reason. Marginally, the cost of driving 5 miles is quite a bit less than $1.
Upto 0.7 per mile I think? That includes an allowance for depreciation so it's not really a true marginal cost, however for a moment let's assume it is. If the bus was $3 do you think it's wise that it's cheaper to drive a 4 mile journey than take a bus?
