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