> But this doesn't scale because the demand is not spread out during the day -- absent carpooling, you still need one car per person twice a day, meaning the supposed savings don't exist.

Very rare for my neighbour to be using her car at the same time I use my car. Not every car driver commutes 5 days a week 9-5.

I work from home, have done for years, my neighbour is retired.

I guarantee in my village there will be at least 10 unused cars at any point during the year, probably nearer 50. There certainly aren't that many empty houses