(ROBERT GALBRAITH/REUTERS)

But that’s not the whole story. As Adie Tomer finds in this new Brookings report, a significant chunk of the nation manages to go carless — more than 7.5 million households in the top 100 biggest metropolitan areas. The New York-New Jersey-Long Island area alone contains 2 million zero-vehicle households — a whopping 28 percent of the population. Next up is Chicago, with 400,000 zero-vehicle households, or 5 percent of the population.

Now, granted, some people manage without cars because they live in Manhattan apartments and can avail themselves of the excellent subway options. But that hardly describes the entire country. For the most part, the carless population tends to be poorer: Low-income households make up 60 percent of carless households. Owning a car is, after all, a pricey enterprise.

But is this really a problem in any way? Don’t people have other options besides cars? Well, sort of. For one thing, some 700,000 of these zero-vehicle households don’t actually have access to transit options, suggesting that there are sizeable gaps in metro transit systems that could stand to be filled in. But set that aside. Another relevant fact is that the typical household without a car can only reach a small fraction of the jobs in the metro area.

That’s why, as Yonah Freemark argues, there may be good reasons for cities to expand existing mass-transit networks. Chicago, for instance, is pursuing the construction of a bus-rapid transit network. Right now, in Chicago, just 39.2 percent of the car-free population can reach 40 percent of the metro-area jobs within 90 minutes — significantly less than in New York City or Los Angeles. (It also helps explain why so many people opt to buy cars in the first place.) Freemark argues that part of the problem is “the radial orientation of Chicago’s existing network makes it difficult to get to jobs outside of the Loop.” But it’s an example of how a lack of transit options can cut off a good fraction of households — primarily low-income households — from job opportunities.