Driving costs vs. transit costs

[SewerRat]

I get that car ownership is expensive and commuting to work is expensive. I've see the per mile costs of commuting to work, but it's hard to tell what they mean. E.g. I read on MMM that it's $0.51 per mile (or something).

But does that include the full cost of car payments, insurance, gas and wear and tear? What is just the cost of gas plus wear and tear. I ask because whether I drive to work or not I'm going to own my car. So, the question is:

Given that I own the car anyway, is it cheaper to drive to work or take the bus?

I have an 22km daily round trip commute (14 miles), so bus fare is definitely more than the cost of gas per day. Does it make any sense to take the bus rather than drive?

[I'm a red panda]

There is a difference between the IRS reimbursement rate, and the actual rate to drive your own car.  You would have to figure out that data specifically for the vehicle in question.

[Wintergreen78]

That 51 cent/mile number is supposed to include depreciation, insurance, maintenance, etc. I agree that the real costs per mile are probably lower if you decide you need a car either way. But, it is hard to figure out a real per-mile cost.

My experience has been that you do save quite a bit by keeping your car parked as much as possible, even if you still need to own it for occasional use. I’m on a once a year oil change schedule, driven more by time than miles, I seem to get about four years per set of tires, and I’m not sure how long it’s been since I’ve replaced brake pads. I’ve had my car twelve years, bought it new, and it still feels like a nice car inside. Even beyond mechanical wear and tear, I think the dirt, food scraps, and other grunge you pick up inside a car when you daily drive it make it feel old. When you keep the inside feeling nice, it is a lot easier to keep using it for years and years. Since depreciation during the first 5-10 years is such a big part of the cost of having a car, being able to keep it longer saves a lot.

[Arbitrage]

Yes, you own the car anyway, but that doesn't mean that the only reduced costs are gas and maintenance.  You can keep the car for longer if you're not driving it much (lower depreciation rate, or replacement costs amortized over longer).  Your insurance rate can be lowered if you don't drive it much - I started biking to work and got my rates lowered by $300/year. 

There's also the question that you might not want to ask yourself, but is valid - if you're not driving much, do you need the same car, or would an older/less nice model give you what you need?  You might find that if you spend very little time in your car, having a nicer, newer model isn't as important as it used to seem.

Current IRS rate is 54.5 cents/mile.  As noted, your personal cost may be lower (not that hard if you're trying), but could also easily be higher for higher-end cars.