The marginal cost of cars is not just a function of mileage. There is non-trivial wear from just sitting, and you have to pay interest on the capital cost. This is at least 5% operating cost per year which is mostly eliminated with shared vehicles that are operated continuously.

Not just but mostly. The biggest time-based costs are:

- Insurance. Some policies have surcharges or discounts based on mileage but it's mostly an annual cost for a typical driver. (Plus excise tax and state inspection.)

- In northern states, corrosion due to salt in the winter happens even if you don't drive a car many miles. My Honda dealer is always amazed when I bring in my old '97 Del Sol with minimal rust; I've just garaged it in the winter for about the past decade.

- Some fluid, belt, etc. maintenance is time-based

- If you want to have a relatively late model car then of course that's a time-based cost. But, if you hold onto a car until it becomes unreliable/expensive to operate then you're back to auto costs being mostly a result of mileage.

Whether costs are mileage or time based vary heavily on the environment.

They don't salt the roads in the winter in Silly-Valley so maintenance costs are primarily mileage based.

In somewhere like NY it's going to be more time based because the vehicle will corrode at a fairly steady rate and salt solutions will counteract lubricants in places that can't be cleaned out (e.g. wheel bearings and ball joints) at a fairly fixed rate.

Yea, I was trying to be extremely conservative with my 5% number, and I think it's much larger due to some of the effects you mention. But I'm a little skeptical time effects are actually larger than mileage ones in total. Do you know a good quantitative argument (even if approximate) for this?

I'm arguing that mileage effects are much bigger unless you regularly flip cars when, say, a lease expires.

AAA publishes car ownership cost numbers. But the big challenge of quantifying this in general is that the relatively fixed component is a lot more for someone who gets a new leased vehicle every three years vs. someone who owns a car for 10-15 years and 150K miles.

http://newsroom.aaa.com/tag/driving-cost-per-mile/

Oh, sorry I misread your comment. Yes, I agree that mileage costs are probably larger than time costs.

My 2003 Honda carries a $1000 maintenance cost per year. Capitalization costs went away well over a decade ago.

It’s still cheaper.

Huh? You paid X dollars a long time ago for the Honda. If instead you and your identical neighbors had been sharing a sequence of Hondas which were driven continuously and then replaced, your contribution to the purchase prices (i.e., the total price of all those cars divided by the number of neighbors) would have been less than X dollars (since your Honda is still running). Furthermore, it would have been spread out in payments over 14 years rather than being paid upfront in 2003. Therefore, you could have kept that money in the bank stock market earning interest.

That's the cost I'm talking about. The maintenance cost of raw sitting time (rust, freeze-thaw cycles, etc.) are additional.

I’m almost 40, live in upstate New York (ie. Cold, snowy). Maintenance for a regularly driven car is all about mileage. Suspension and electronic motors start falling off at $150k miles.

Per mechanic friends, most better cars go until about 250k miles with modest maintenance issues, and after that things like transmissions fail and are not a good value.

The problem with the pooling is that any outlier blows the financial model. Whatever interest I would make would be wiped out by a single event where I’d need to rent a car.

There’s a place for things like Uber (or traditional taxis) and zip car. But unless you barely use a vehicle or cannot afford one, it’s a pain in the ass to share.

I'm not making any claims about the overall value of ride-sharing an autonomous vehicles. I'm only rebutting the idea that the cost of capitalization are trivial.