I was thinking about this, and what I’ve come up with is that all cars that spawn outside should be in very poor condition, only good for scrap with perhaps a fully intact component or two once every few cars. There will be a chance of finding a fully intact vehicle in garages (and perhaps modify the house floor plan to occasionally include a garage that has a chance of an intact car), but this is America, there should be roughly 2.5 cars per household*.
So end result, fully functional cars slightly more scarce than they are now, but a more convincing number of car hulks scattered all over the place.
And to make the post slightly on topic, the rationale would be that the first waves of acid rain were much more potent, and totally corroded all exposed vehicles.
*The cars wouldn’t necessarily be at the house in question, many would be in parking garages, parking lots, even those small ones in front of some shops, and some would be on the roads or the side of the road.
