I don't know if anyone mentioned this idea yet, but maybe for cars to be usable, players would just have to build a drive way on the lot, and whatever car animations that happen take place on the lot, so it would look like the car is pulling out from the lot but then goes to a loading screen before it actually goes anywhere, for lots that don't have this drive way the car will just end up in the sims inventory, and for lots that have a pre built parking space the car will pull into the drive way. Ya the issue here would be that it would take up space on the lot, but I think this would be a good way to implement cars.
