Like many Americans, both my wife and I probably weigh a little more than we should, so we tuned in May 14 eager to see what the series' diagnosis was for the American physique. We expected—and got—the "nature vs. nurture" recap and the genetic variables and the need for both diet and exercise, backed by plenty of serious and credentialed talking heads.

We also got—trains! Right up front, images of a New York City Transit subway line (elevated) and a SEPTA trolley trolling the streets of Philadelphia were prominently displayed. The verbal message identified lower-income people in various urban neighborhoods being overwhelmed by obesity problems, with maps and data to prove it. But even if one is focusing on poor urban locales, why dramatize trains?

"Where are the cars? What about the cars?" was uttered not by the Railway Age Managing Editor, but by his wife (sentenced to drive 75 minutes per day, twice a day, to and from work).

Indeed. I'm fully aware that any causal link between driving and obesity remains for now, at best, disputed and contentious, in a category akin to climate change, evolution, or free-range parenting. Still, it is now subject to open discussion—but not by the HBO show on American obesity, apparently.

When the show finally got out to the "real America," it found overweight and obese people there, too, of course, and more experts bemoaning lack of physical education in schools, video game zombies, lackadaisical (and often overweight) parents, etc. The Texas state comptroller, in particular, made an elegant case for combating obesity on economic grounds, acknowledging the Lone Star State has a serious obesity problem—props to her.

But no shots of the highway or the main street—at least, none with any volume of traffic on them. Almost no cars at all, not even in the background. Why not? Trains are more picturesque? More exotic? More quaint?

Sure, you can find overweight people on trains every day, and colleague Luther Miller vouches for that on his daily rides aboard the No. 1 train. After all, here in Manhattan, we have more McDonalds per square mile than anywhere in the world (according to the 2004 movie Super Size Me). So there is a correlation of some sort. So one might posit that maybe trains help make one fat. (Credit Luther Miller for asking the title question above.)

But if they do, then the door opens to queries on other forms of transport, like those long, daily car grinds endured by sedentary drivers.

HBO visually opened that door, and so far as I can tell has chosen not to walk through it. Talk about not exercising. The series is in four parts, so it’s quite possible I missed the discussion (however brief) I’m looking for; if you found it, feel free to let me know at dbowen@sbpub.com.