Is this post from the Freakonomics blog pretending to be more clever than it really is? Yes. Does it employ an annoying, I’m-pissing-off-both-sides-I-must-be-such-an-impish-devil angle? Yes. Must it die? Yes.

Its conceit is that, measured in terms of how much energy it takes to move a human body a given amount of space, public transit—especially buses—is not necessarily more energy efficient than private cars in contexts where it’s not used very much, and therefore spends most of its time running around half empty.  (This is, incidentally, ground that the Straight Dope covered more thoroughly years ago.)

“It is not clear that moving around large and largely empty vehicles is much of an improvement over moving around smaller ones. In fact,” our Freakonomics correspondent concludes, “it could be worse.”

This is not true. In fact, in the way of blog posts with cutesy counterintuitive ledes, the writer admits it’s not true somewhere towards the middle of the piece: if you include the energy spent building vehicles and infrastructure, even buses are more efficient than cars, and trains are much more efficient.

But even this misses the larger point, which is that public transportation doesn’t have to move people as far, because it allows people to live more densely, and therefore closer to work and stores.  It’s nice if it’s more efficient on a per-mile basis, but even when it’s not, you usually get fewer carbon emissions because people just don’t have to travel as many miles. If you’ve built a neighborhood that’s dense enough for people to walk to school or a corner store instead of driving, you’ve reduced the number of miles traveled even further.

Of course, if you build and run transit in such a way that you are not encouraging—or allowing—people to live more densely, you lose that benefit. This is why people like Ryan Avent are up in arms about laws that specifically prohibit people from building bigger apartment buildings, or even more tightly spaced houses, near public transportation when there’s demand for it. (Actually, he’s more upset about the economic consequences of that, as am I, but the causal idea is the same.)

Anyway, this reminds me of an insight somebody had—I forget where I read this—about the fact that most American public transit projects at the moment are either commuter-style light rail that goes way into the suburbs, or very short streetcars that circulate around a popular central district. Neither of these is ideal from a user perspective—the commuter rail is usually surrounded by a giant park and ride lot, and is useless for getting anywhere other than downtown; and no one is going to use a mile-long streetcar for anything, especially when the frequency is so low that you could walk to the end of the line before the next trolley came—but they’re even worse when you consider that they’re failing all the environmental tests, too. They don’t really encourage people to live densely, since the light rail just chases sprawl farther and farther away, and the streetcars are too short to be a primary mode of transportation; plus, because they’re so unuseful, they’re likely to spend much of their time running around mostly empty. (Consider that none of the seven commuter rail projects to open in the U.S. in the last ten years serve over 6,000 people a day, and three carry fewer than 2,000, even though on average they reach 30 miles outside of downtown. More traditional light rail systems are generally above that, but still have pathetic riders-per-mile numbers.)

It’s not hard to figure out why we’re building such nonsensical things, though: That’s where the middle class people live. With American cities moving towards a sort of donut-shaped geography of poverty—wealthy districts at the very center and in the suburbs, buffered by working class and poor urban districts and inner-ring suburbs—the political momentum for building the kind of tight but comprehensive in-city transit networks that are ideal from a user and environmental point of view is pretty limited. This is a major reason to be skeptical of urbanism as “creative class” catnip: It tends to skew planning away from what density and transit is actually good for, not to mention what is economically just.

(I feel the need to note, as a postscript, that on this count, the CTA deserves credit—its major projects, like BRT on Jeffrey, Western, and Ashland, are exactly the sort of mid-range workaday operations that will increase mobility and allow greater density outside (as well as inside) gentrified central districts. Neither wacky extensions to the suburbs, nor pointless circulators downtown, are among its shortcomings.)