Below are two different excerpts from his new book, first, an introductory personal essay and then, a look at density as just one of several components of successful transit.

I live in Houston, Texas, a famously car-oriented city. I work at an urban planning practice, teach at Rice University, and serve on a transit agency board. I can do all of that on public transit. Almost every morning, I walk out my door, go three blocks down the street, and get on a train. It will take me to work, to meetings, to lunch with friends, to medical appointments, to lectures, to museums, to the park. I find it as convenient as driving, and considerably more pleasant. Transit makes my life better.

This is possible because the transit I live next to is high quality. The train runs every six minutes during the day on weekdays, so I rarely have to wait. It has its own lane, and traffic signal priority, so it’s not slowed down by congestion. My transit system has nice stations that shelter me from the rain, and good passenger information.

But, most importantly, taking the train for most of my travel is possible because the transit I live next to goes to the right places. It runs by lots of apartments and condos and houses, presenting me with options for living next to it. It runs by lots of office buildings, including the building where I work. It also runs by a lot of the other things I want to do in my life—socialize, learn, have fun. At all of those places, the train drops me off right in the middle of things, not in a giant parking lot or in the middle of a freeway.

More people ought to have the choice to live like this. I’m on the train every day with lots of different people, who live in different places and work in different kinds of jobs. This transit line works for them, too. Good transit offers access, opportunity, and freedom.

People who don’t ride transit benefit from transit, too. People who use transit—be they downtown professionals or minimum-wage service workers—are essential to the economy. Everybody on a bus or a train represents one less car on the road. Public transit significantly reduces the environmental impacts of cities, reducing energy use and preventing sprawl that eats up natural habitat. All of these benefits scale with ridership—as people use transit more, its societal benefits increase.

To build good public transit, which is transit that is useful to lots of people, we need to have the right conversations about transit. We need to talk about what matters—to focus on the quality of service, not the technology that delivers it; to talk about all kinds of transit riders, not just about a narrow target market; to understand that the transit experience depends on buildings and streets and sidewalks as much as it does on stations and trains; and, above all, to talk about getting transit in the right places. We also need to be willing to talk about where transit is falling short. The measure of success in transit is not miles of track or ribbon cuttings, it is whether transit makes people’s lives better. It is remarkable how much of the public transit we build in the United States doesn’t go where people want to go or when they want to go there. Some cities have built transit that has transformed the experience of living there. Some have simply built a lot of transit. Some have built very little. It is worth comparing them and drawing lessons. That’s what this book is about.

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Density

Nothing matters as much to making transit useful and successful as population density. Every mile of transit costs money to build and operate. Fundamentally, the usefulness of that mile is a based on simple math: how many people will that mile of transit reach? A mile of route puts roughly a square mile of area within reach of transit. If 100 people live in that square mile, there are 100 potential transit riders; if 10,000 people live in that square, there are 10,000 potential transit riders.

Multiple research studies have attempted to quantify density thresholds for transit. At somewhere around 3,000 people per square mile, it makes sense to operate some level of infrequent local bus service. This level of density is common in US cities, both in prewar neighborhoods and postwar car-oriented suburbia. Here, while an hourly bus will get ridership, transit will never be the most convenient mode, and most people will choose to drive. Somewhere around 10,000 people per square mile, though, transit reaches a tipping point. Here, the sheer number of people are enough to justify frequent service. Moreover, walking and biking become useful for short trips, which makes it easier for people to live without cars and makes transit more desirable. As densities further increase, more and more transit is justified. The transit- oriented neighborhoods of older cities have over 15,000 people per square mile, and even newer car-oriented cities like Los Angeles and Houston have some neighborhoods at these densities.

The performance of a rail or BRT line is directly related to the surrounding densities. For example, the most successful light-rail systems in the United States—San Francisco, Boston, Philadelphia, Seattle, Newark, Jersey City, Buffalo, and Houston—serve large areas of over 10,000 people per square mile.