I would also guess that percentage of housing units would be substantially higher if you limited it to homes also owned by people with cars. Both because owning

I would also guess that percentage of housing units would be substantially higher if you limited it to homes also owned by people with cars. Both because owning a garage is a lot more desirable if you have a car and homes with garages are in places where people need to drive to get around: there are millions of people in major cities who own neither and have no need for a car.