I’m concerned, of course, that Americans have built a society with so few buses that everyone has to buy a car on credit. But being “underwater” is not the main problem here.
More specifically, we've built cities that are pretty awful for bus (or rail) transportation, if you thrown any sane amount of money at the public transit system. Most of our cities have been relying on inefficient (i.e. very spread-out, low-density) growth patterns to cover costs, while the long-term expenses demanded by that growth (maintenance, for example) outpace the revenue it brings in. It's musical chairs, and when the music (growth) stops most of the cities in the US are going to be Detroit, with way too much city for their tax base to support.
Huge, low-density cities lead to shitty, expensive services (bus service being but one example) and crippling, indefinitely-ongoing maintenance expenses.
Perhaps we can mitigate many of our urban problems--pollution & greenhouse gases, road congestion & traffic accidents, and consumer debt--by investing in electric or NG buses.
That said I tend to agree that "underwater" isn't really the right concept for a car loan. Unless of course you total a car right after you get it. Sucks to be putting $ towards a car note with nothing behind it.
In my early years I once took out a loan for a car. I've never once been underwater on my loan. You're only underwater at some point if you put down a small/no down payment and pay the minimum amount due every month.
The topic of this article is people rolling the balance of their previous car loan into their new car loan. So they are underwater before they drive it off the lot, sometimes by a LOT. That's scary! Its basically running on a treadmill that always accelerates.