This data is from 2019, but I imagine that things would look pretty similar today and that it might even be a little more pronounced. The dataset from the above article looked at how many people have cars in a given area (a darker dot = fewer cars) and then plotted this against population density and income per capita.
Here's what that looks like for the regions of New York, Boston, Los Angeles, and Houston (data from 2013 to 2017):
What is fascinating about these charts is that they show two different correlations. In dense and transit-rich cities such as New York and Boston, car usage is most closely linked with population density and not with income. The dark dots form a horizontal line near the top.
However, in the case of Los Angeles and Houston, car usage is instead most closely linked with income and not with population density. The dark dots form a vertical line near the left -- the lowest income per capita.
So what does this tell us?
It tells us that if you design a city to broadly require a car, then you are likely to sort people based on those that can afford a lot of car and those that cannot. On the other hand, if you design a city around transit, then you are likely to instead create a place where both the rich and poor get around in similar ways.
There is also evidence that the latter is being increasingly viewed as more desirable. 2017 was the first year in the US where high-income young people (ages 26 to 33) drove less than low-income young people. Presumably these high-income people had choices, and so I tend to view this as a preference.
As a whole, this is surely a good thing for our cities. But now I think we need to be careful not to allow density and walkability to become the new luxury that only the rich can afford.
The headline, here, is that "the US is running short of land for housing." But if you read the article, you'll see that the headline should probably read, "the US has land-use restrictions in place that make it unnecessarily difficult to build enough new housing." Here's an excerpt:
Asking prices for homes in these new communities [the exurbs of Tampa] go as high as $900,000, in part because the land underneath is so valuable. That has a lot to do with land-use regulations.
Tampa’s zoning rules prevent developers from building anything larger than a single-family home in much of the city. When officials for Hillsborough County, which includes Tampa, adopted zoning regulations in 1950, they said the measures were necessary to prevent overcrowding and traffic jams and would preserve the neighborhood character, all “with a view to conserving the value of buildings,” according to the regulations.
If all you can build are single-family homes, then you're going to need a lot more land compared to if you were allowed to build a bit higher and/or a bit denser. But it is a good way to ensure that supply remains somewhat scarce and that one is faithfully "conserving the value of buildings."
It is, however, worth mentioning that we have invented ways to use land more efficiently. The population density of Hillsborough County is somewhere around 1,200 people per square mile. The population density of Paris, on the other hand, is over 50,000 people per square mile.
Somehow people still enjoy Paris.
The relationship between car ownership and urban density is a fairly intuitive one. Below are two charts from a study by Francis Ostermeijer, Hans Koster, Jos van Ommeren, and Victor Nielsen, showing how urban density is inversely correlated with car ownership. In other words, the more people with cars, the less dense that a particular place is likely to be.
But there's an interesting chicken-and-egg question here. Does Atlanta, which is near the bottom right in the above chart, have a lot of cars because it wasn't dense enough to support other modes of transport, or did the prevalence of cars in Atlanta cause the city to spread out and become less dense? And that is exactly what the above researchers set out to determine.
To do this, they started by looking at the presence of commercial car manufacturers in the above geographies in the 1920s. One of the things they found was that having a car manufacturer in your city at this time appears to have had no effect on population density. But over the long run, rising car ownership seems to have had a sizeable effect on reducing population densities in those places.
The conclusion they draw from this is the title of this post: cars have made cities less compact, rather than low population densities causing people to go out and buy more cars. This makes some sense to me because cities were doing just fine before we invented cars. But like all transportation innovations that allow us to move faster over longer distances, the car encouraged decentralization.
There are, of course, all sorts of possible implications for a finding like this. But the authors specifically mention developing countries where car ownership may still be relatively low. This is something to be mindful of because if you put most people into cars, history strongly suggests that it will impact the kind of city that you end up building.