I recently finished reading Railtown, by Ethan Elkind. It’s a history of the Los Angeles rail transit system, and I liked it so much that I decided to read another history of an urban rail transit system: 722 Miles by Clifton Hood, which tells the story of the New York City subway.

In comparing the two books, what is remarkable to me is the difference in what motivated these two urban rail transit systems, one built between 1888 and 1953 and the other built beginning in 1985 (and continuing to grow).

In Railtown, we read about how some of the reasons for bringing urban rail transit back to Los Angeles were to combat congestion and sprawl. This echoes the arguments in favor of transit, and especially rail transit today – that rapid transit will support compact, high-density development that will allow people to be less reliant on cars.

In 722 Miles, we read about how the subway was first proposed in the 19th century, not to support greater densities, but to combat density. Lower Manhattan had become too crowded, and then-Mayor Hewitt of New York City hoped that a rapid transit system would spread growth to the less-densely populated areas of Manhattan and the Bronx to the north.

So, in the century between the construction of the New York City subway, and the Los Angeles Metro Rail system, the popular view of rail transit turned 180 degrees from being a way to create sprawl and disperse density to being a way to combat sprawl and create density. What happened? Cars.

When the New York City subway was first proposed, there weren’t really cars (the Model T Ford wouldn’t arrive on the scene for another 20 years or so). If there were, perhaps Mayor Hewitt would have proposed to disperse Manhattan’s population by building a highway (as Robert Moses did through Long Island just a couple of decades later). But in the late 19th and early 20th century, the attractiveness of urban rail was that it offered an alternative to walking. With rail, it was no longer necessary to live within a mile or two of your workplace, so you were free to move further away to where you could have a little more space.

Today, basically everyone has a car. According to this study by Michael Sivak at the University of Michigan, fewer than 10 percent of all households in the United States don’t have a car (although this proportion seems to be increasing). Based on the 2009 National Household Travel Survey, over 80 percent of all trips in the United States are by private vehicle, compared to about 10 percent of all trips that take place by walking. So transit is no longer about replacing walk trips and allowing people to live farther from their destinations. Now, it’s about replacing driving trips and allowing us to put all those destinations closer together, without having to make space for moving cars on wide roads or storing them in expansive (and expensive!) parking lots.