This is less applicable to those who wish to sell off their vehicle and abandon car ownership entirely, but few people are willing to take such a leap without trying a car-lite lifestyle first. For those who just want to dip their toes in the water, to try something between complete car dependence and complete transit dependence, using public transportation isn't so much a replacement and reduction of costs as it is an additional cost. Not only do you still have to pay for insurance and some gas, you now have to pay for bus fare as well, and suddenly the savings don't seem like such a great deal compared to the relative inconvenience of transit (excluding the few places in the country where transit is actually more convenient). It's a catch-22: as long as you're holding onto the car you're not saving a lot of money, but unless you're saving a lot of money you may not be convinced to get rid of the car.

This problem is compounded by something I'm calling "Sunk Cost Bias," the tendency to try to make the most of your investment by driving more. This may sound foolish since the more you drive the more the costs pile up, but, in a way, it's also perfectly sensible. After all, the more miles you get out of your car, the lower the per-mile cost of ownership. And if you've already got the car and don't have a monthly transit pass, a trip on the bus or train can actually cost more than driving if you're only going a short distance.

We all know that public transportation is a less expensive way to get around that owning and driving a car, but what's less appreciated is that it's not a straight line from one extreme to the other. The jump from car-free to car-lite is massive. In reality, the spectrum of car usage and costs looks something more like this: