The authors used satellite and other data to inventory parking spaces on-road and otherwise in 5 US cities of wildly varying size. In four of the five cities, there were more parking spaces than humans, and the the land value of those parking spaces ran into the billions of dollars in total and tens to hundreds of thousands per resident.Scharnhorst finds that there are more than 2 million parking spaces in Philadelphia, 1.85 million in New York, 1.6 million each in Seattle and Des Moines, and just over 100,000 in tiny Jackson, which has a population of about 10,000.
Parking takes up a huge amount of space: Jackson has more than 50 parking spaces per acre, 25 times its residential density of just two households per acre. Jackson has a whopping 27 parking spaces for each of its households.
Parking obviously isn't solely to blame for high rents or housing crises - New York is by far the least over-parked city on that list and still has some of the most expensive housing in the world, but Seattle's problems surely aren't helped by having $35 billion dollars of land locked up in providing 5 parking spaces per household.
As mentioned here a lot of this absurdity is down to poorly designed zoning laws requiring developers to build a certain number of parking spaces regardless of whether it makes sense for them to do so. It acts as a subsidy on driving (in that parking is cheaper than it would be in an unregulated system) paid for by the lost economic activity or housing the land could've been used for, and it even hurts drivers by encouraging more people to drive and thus further congesting cities, raising commute times and air pollution.