The cost of driving

Imagine you want to travel from Los Angeles to San Francisco and back again. For argument's sake, let's say a round-trip plane ticket cost $150.  Would it be cheaper if you drove?

To figure this out,  you need know the cost of driving. And I don't just mean the cost of gas. There's also the cost of maintenance and deprecation. Well, some of the depreciation.

This is a trickier subject than I expected when I started considering it. For one thing, note that the cost of driving is different than the total cost of owning a car. Just to own a car, you need to pay registration fees and insurance. But those are (mostly) fixed costs that vary little, if at all, with how much you drive. Should they be part of the "cost of driving" calculation?

There are various web pages that will give a rough estimate of the cost of driving. But I really wanted to know my specific cost, for my car, right now. I own a 2011 Hyundai Santa Fe with 101,000 miles on it. What is it costing me? 

Gas: Fuel may be the easiest cost to calculate. My car gets about 22.5 miles per gallon, according to the readout on my dash. This is an average, of course -- on the open road, the MPG will go up; while idling in city traffic, it will go down.

When I bought gas the other day it was $3.39 per gallon. Divide the the cost of gas by the MPG, and we get ... 15 cents per gallon. That's my driving cost for gas.

Oil changes: I get an oil change about every 7,000 miles. These days it costs about $42 each time.  That works out to 0.6 cents per mile. Not much.

Tires: How long do tires last? This varies widely, but in my experience, I get about 70,000 miles on a tire. (Your mileage may vary. Literally.). And how much do tires cost? Angie's List members reported an average cost of $637 to replace all four tires in 2015. Four years later, I'm going to say $700. This works out neatly. Divide $700 by 70,000 miles and you find that tires add one penny per mile.

Other maintenance costs: Cars need maintenance. Things break and need to be fixed. Brakes, belts and fluids need to be replaced. It's hard to figure all those, so I'll take a shortcut: AAA says that a medium-sized SUV like mine incurs maintenance costs of 8.6 cents per mile. That would include the oil changes and tires I listed above. (You might wonder why I figured those items separately if I was just going to add them into the general maintenance cost. I'm wondering that, too.)

Depreciation: Things get tricky here. Each mile that drive your car lowers its value and takes you closer to the out-of-pocket cost of buying a new car. But your car also depreciates even when you're not driving it.

Depreciation will vary widely depending on the age and value of your car. But I'm only interested in my car.

I went to Edmunds.com and found that my car currently has an estimated value of $5,675 in a private party sale. Then I added a fictitious 20,000 miles to the car's mileage, and Edmunds reduced the value of my car by $532.  Divide $532 by 20,000 miles and I find that the depreciation is 2.7 cents per mile.

That's much less than I expected, but looking at the numbers I see that age, regardless of mileage, is a separate factor in car value. For instance, just by adding a year to the age my car -- but not changing the mileage -- the value drops from $5,675 to $4,940. 

Conclusion: Remember that my goal was strictly to discover the cost of driving. The additional costs of ownership (insurance, registration and part of depreciation), are important, but they're not the subject on the table.

The cost of driving my car is 15 cents per mile for gas plus 8.6 cents per mile for maintenance plus 2.7 cents per mile for depreciation. Total: 26.3 cents per mile.

Driving roundtrip from L.A. to San Francisco is 764 miles. That's $200.94 in driving costs. That's more than the air fare. But if you're thinking of flying, remember to figure in the cost of getting to and from the airport!