I've bummed a ride home (in a car! the beauty of commuting on a folding bike) a couple times this winter during exceptionally bad weather or late workdays when the siren call of a warm, faster commute pulled too strongly to ignore. The co-worker from whom I've accepted rides mentioned last week that she had calculated that as long as she continues to car pool with another co-worker of ours, their combined costs for the car commute are less than the cost of two annual transit passes, even with the passes partially subsidized by our employer at a rate of around 35%. This sort of argument is one I've heard before, a different aspect of the siren song of automobiles, and I had a feeling that in this case, as in many others, it was based on an incomplete calculation.
I know this because during the process of selling our car I wrote a maintenance record summary in a spreadsheet as a service to the new owner as well as for my own records (I also gave the new owner my file of all the receipts and reports). Combining these tabulated maintenance costs with records of our insurance and registration payments, depreciation based on the actual purchase and sale price of the car, and a reasonable guess at fuel costs (using recorded distance driven, measured fuel efficiency, and average fuel price), I made a realistic estimate of the total cost of owning that car for almost exactly 5 years.
Make/model: 2001 Ford Focus ZTS sedan, 4-cyl, EFI, 1.8L, FWD
Primary place of use: Upstate NY
Primary mode of use: 24-mile round trip year-round 6-day per week commute on country roads (4-years)
Other use: Occasional trips to nearby cities, 3 cross-continent road trips
Special equipment/costs: Excellent snow tires ($600/set, two sets), ~$2000 extra repair due to driving on salted roads.
Length of ownership: 5 years
Total distance driven: 52373 miles
Maintenance, repairs, and tires: $6685.51
Value depreciation: $6000
Fuel (28 MPG, $2.60/gal): $4863.21
Insurance (2 drivers): $2760
License & registration: $90
Total cost of ownership: $20398.72
Annual cost of ownership: $4079.743
Cost of ownership per mile: $0.39
The estimate is large. Much larger than most people realize and much larger than I had realized until I finally tabulated all the costs. This accounted for almost 10% of our household income, spent to have the use of a single car. This estimate is also conservative, it doesn't account foe a few oil changes that happened in other states and the receipts didn't get filed, and the estimate of average fuel price is undoubtedly low. Most of the time it was much closed to $3.00/gal. Note that the current reimbursement rate for mileage on a personally-owned vehicle is $0.50. When most people see such a rate they think of it as exceptionally high and think they're getting paid to drive, when in fact our costs for a small, inexpensive, relatively efficient car were almost 80% of this figure!
This isn't to say that we didn't get something for our money. By being able to commit to a car commute (a dubious decision in hindsight) we were able to buy a house in an area with we could afford. On the other hand, before we moved out of town (our first year of owning the car we lived in town in a rental and only used the car for grocery and errand) we only put about 4500 miles on the car, after that we put on almost 12000 annually. The difference between these numbers is almost exactly the length of our 6-day/week commute.
Making another reasonable estimate that half of the depreciation can be counted as mileage-based and half as time-based (a car that isn't driven doesn't lose value as quickly) while counting maintenance and fuel as purely mileage-based and insurance and registration and purely time-based, it comes out that about 71% of our costs were based on mileage and 29% were based on time-owned. This means that if we hadn't moved out of town our annual car costs would have been $2420 instead of $4080. The incremental cost of our commute was $1660 per year: 40% of our total cost of owning the car.
To me, this drove home the point that if you're going to own a car anyway and you carpool driving can be cheaper than an annual transit pass costing around $1000 per year per person. This is one of the financial traps of car ownership: the incremental cost of any extra usage is small enough that if you own a car it's hard to financially justify not using it. It's a pair of thrifty handcuffs, making the owners feel good about driving more. I consider this throwing good money after bad.
By using car rentals and car-sharing instead of owning our own car, we incur something very close to the actual per-trip cost of car ownership, but structured such that the overhead (the time-based costs) are paid on a usage basis. This shifts the thrift decision from saving money by driving more to saving money by driving less.
The financial incentive to not drive can't be entirely realized by not driving. It's realized by not owning a car. This is a huge psychological hurdle that can be difficult to get over, and there needs to be plenty of shared infrastructure in place to make it happen: good transit, convenient car-sharing, and walkable/bikeable everyday shopping were keys to getting over that hurdle for us. Once we had structured our lives to be able to take advantage of them, the financial decision to sell the car was easy.
As an aside, when I've succumbed to the offer of a ride home, traffic has always made it take longer than taking the train.