The true costs of driving-- how much could you save on transportation?

Could you save money by switching from a driving commute to a transit (and/or carpool/biking/walking) commute? There are more costs to be considered than simply the price of gas, and these calculators will help you figure them out:

• For a simple approach, the American Public Transit Association has a handy calculator which lets you plug in your commute mileage and enter the precise gas prices, MPG, parking costs, and public transit costs that fit your situation. It also includes (based on the size of your car) an estimate of the increased expenses per mile you drive for maintenance and tires, an important addition that often gets left out of back-of-the-envelope calculations. Check it out here.
• This calculator is similar to APTA's, but lets you customize the value for maintenance/tires, and has a field for per-mile savings on depreciation/insurance/taxes/financing.
  
• If you want to get more detailed there's a really cool "Car-Free Diet" website (sponsored by Arlington, VA but it works fine for people anywhere.) It not only explores the cost of driving vs transit/carpool/walking/biking, but also the calories you could burn by walking or biking, and the environmental benefits as well. It's extremely customizable-- from picking the actual make, model, and year of your car, to entering up to 3 different driving routes at a time, to including your weight and age for the calorie-burning calculations! Then you can see numbers and graphs for the money saved, calories burned, and CO2 emissions reduced if you changed each trip to transit, carpooling, biking, walking, or telework (ie "What if I took transit to work twice a week and walked to the grocery store on Sundays?") It's a pretty incredible tool-- check it out here!
• And if you want to take it a step farther and really explore the externalities (costs that are borne by people other than yourself) of your driving, try this calculator called The True Cost of Driving. Not only does it add a few other factors to your personal driving costs such accounting for the average cost per mile of car accidents (health care and property damage), but it also lays out things like how much the government pays for highway maintenance, repairs, and waste clean-up per mile driven; a variety of pollution impacts per mile driven; and a bundle of other effects your driving has on society.

How much does your transprotation cost you? Have you run the numbers recently? How do you do your calculations? Is there anything these calculators are missing?

If you're thinking about switching, check out:

• Paying for transit with pre-tax money
• Free cab rides home in emergencies
• Financial incentives for new carpoolers