Housing and transportation are two different issues, right? Some places have dense urban forms, while others are suburban or rural. Meanwhile, in some places there's a lot of walking or biking or transit use, and in others, people drive everywhere. Right?

Not really, this graph demonstrates. Instead, the two are one.

London, New York, Boston, and Philadelphia are different in many ways, but how many own cars is consistent between them. It's not about which side of the Atlantic you are on, but how dense your neighborhood is.

This graph doesn't show the causation. Some places can be dense because they are around a rail station. Cities tend to build better sidewalks and bike lanes and run more buses to places that are already dense. If an area doesn't have non-car transportation choices, people won't be willing to live in denser urban formats in most cases, because they'll insist on lots of parking and road space.

“The best transportation plan is a good land use plan”

Portland discovered the same phenomenon when trying to achieve a goal of 25% of trips happening by bike. Great goal! But, BikePortland explains:

The obstacle to advancing our city to 25 percent of trips by bike by 2030 wasn’t actually the biking, city staff said. It was real estate. “Even in 2035, there are too few jobs too far from housing,” senior transportation planner Peter Hurley had told the city planning commission June 13. In other words: Portland wants to officially concede that its recently approved comprehensive plan didn’t legalize enough density for Portland to join the ranks of the world’s best cities for biking.

Even in the ultra-bikey Netherlands, people follow a similar pattern to British and Americans: They walk for short trips, bike for medium trips, and drive or take transit for longer trips.

How Rotterdammers get around by BikePortland.

Certainly trains can substitute for driving on long trips (and in Europe, they do much more than in the US). The BikePortland analysis clearly shows how many more Rotterdammers ride transit, especially for long trips, than Portlanders do in a city with many fewer train lines. In cities, it's vital to do two things at once:

Build a great network of sidewalks, bike/scooter lanes, and bus or rail corridors Allow more people to live near jobs, stores, and transit

You can't do one without the other. It's a package.