Though this presents a problem in that we're burning through a car 20 time faster, (100% vs 5%). Most cars people own don't last 20 years, so they won't even last a year in the future? There better be some distributed economic system for providing those cars, because that's a large expense.
A car right now needs regular maintenance as it is every few months, even if it's just changing the oil. That will go from months to days if they're being used 24/7.
Actually a car that is driven frequently holds up better than a car that is only driven every now and then, and is left outside for the rest of the time. Cars in almost-constant use will also be taken care of better, and automatically; for example, they will be driven through a car wash automatically regularly, and the automatic oil monitoring system will replace said oil at a machine during 15 minutes somewhere at a point where the demand is lowest. Maybe we'd be burning the car 2 times faster, I don't know exact numbers - but it surely won't be 20 times, and for any multiplier lower than those 20, we come out ahead.
A car right now needs regular maintenance as it is every few months, even if it's just changing the oil. That will go from months to days if they're being used 24/7.