We went from 2 cars to 1. It's problematic at times with two kids and diverging schedules, but we make it work. Even if you own a vehicle outright, if you eliminate the insurance associated with owning the car, as well as the depreciation of owning the car, the equation is easy. I have to say though, at $3.50 +/- per gallon of gas, it shouldn't take too many tanks of gas to pay for most of your annual commuting needs providing that you're going to own a bicycle whether you commute on it or not.