Dear Tom and Ray:

I'm living with a bunch of poor, just-out-of-college/sometimes-in-grad-school folks who are planning to share my car. I don't want to sell it. I'd like to come up with a way to let everyone contribute based on how much they use the car and how they use it. How does highway driving compare with city traffic for wear and tear on the car? It obviously has an effect on gas, but what about the engine and other parts?/p>

-- Dan

RAY: Well, the first thing you should do, Dan, is go down to where the car is parked, and give it a nice, big kiss goodbye. Because the guys who share the car with you are going to ruin it.

TOM: People never treat a shared car as if it's their own. Especially just-out-of-college people. So, if you go ahead with this plan, you at least should be prepared for the car to deteriorate rapidly. You'll find dents that no one can remember denting. You'll find bent rims, even though no one remembers driving up on a curb. You'll find a pile of puke in the cup holder, and no one will remember winning a hot-dog-eating contest

RAY: But if you're OK with all that, then I suggest you implement a flat-rate plan. Our very own federal government has studied this issue in depth -- how to reimburse people for the use of their cars. Their conclusion is that a car costs just over 50 cents a mile to operate.

TOM: Which I would round up to $1.75!

RAY: That's 50 cents a highway mile, 50 cents a city mile, 50 cents up a hill and 50 cents down a hill. According to the Internal Revenue Service, that covers one mile's share of gasoline, maintenance, future repairs, wear and tear, depreciation and new Christmas-tree air fresheners.

TOM: And if it's good enough for the IRS, it should be good enough for you guys. So tie a log book and a pen to the center console, and once a month, bill everybody 50 cents a mile.

RAY: Put the money in an account to cover maintenance, repairs and a down payment on your eventual new car, which I'm guessing you won't be sharing, Dan. Good luck.