While the latest New York Times Magazine paints a portrait of the relatively small slice of the US population that takes long-distance train rides, a recent Brookings Institution report notes that millions of shorter-distance riders have made Amtrak the fastest-growing mode of travel in the US. In A New Alignment: Strengthening America’s Commitment to Passenger Rail, Robert Puentes, Adie Tomer, and Joseph Kane report that Amtrak ridership has grown 55% since 1997 (compared to a 20% increase in air travel), and now carries more than 31 million riders annually.

This renaissance of rail doesn’t reach the entire country, though. The report tells us ten metropolitan areas — in the Northeast, Chicago market, and California — account for nearly two-third of Amtrak ridership. Short-distance corridors generated a positive 2011 operating balance and are responsible for nearly all of the system’s growth, while corridors over 400 miles had a negative operating balance.

At Washington Post’s Wonkblog, Brad Plumer zeroes in on 15 long-haul Amtrak routes (running 750+ miles) that lose nearly $600 million annually. “Many of these were originally put in place to placate members of Congress all over the country, and they span dozens of states,” Plumer explains. “This includes the California Zephyr route, which runs from Chicago to California and gets just 376,000 riders a year.”

Brookings’ Puentes, Tomer, and Kane describe the differences between Amtrak’s two types of routes:

Although a national system, America’s passenger rail network is made up of two distinct types of routes: those less than 400 miles and those greater than 400 miles.

The 26 routes traveling less than 400 miles make up the operationally efficient portion of the network. t includes the two most popular Northeast Corridor routes, the Acela and Northeast Regional, which operate between Boston and Washington D.C., including spurs into Virginia and western Massachusetts. The positive operating balance from these two routes—which currently do not receive direct state operating subsidies—were enough to offset the net operating costs of the other 24 short-distance routes. Those other sub-400 mile routes typically enjoy direct state support (even before the federal PRIIA legislation) and always serve at least one large metropolitan area. In total, these 26 corridors carried 83 percent of all system riders in 2012.

The other 18 corridors traveling over 400 miles represent the geographic equity portion of the network. They include relatively short routes like the Vermonter, as well as the longest current service, the California Zephyr between Chicago and San Francisco. They pass through nearly all 46 states that Amtrak serves, far more than their short-distance peers do. These routes also travel for vast stretches between major population centers and offer service to many smaller, relatively isolated communities with limited intermetropolitan alternatives. However, this regional coverage comes at the expense of low ridership figures: they carried only 17 percent of Amtrak’s passengers in 2012 but, combined, constitute 43 percent of Amtrak’s route-associated operating costs.

The PRIIA legislation they allude to is the Passenger Rail Investment and Improvement Act of 2008, which calls on states to develop state rail plans and requires them to work with Amtrak to develop a formula for states to contribute to the costs of intermetropolitan rail routes. PRIIA doesn’t require state collaboration or financial contributions for routes longer than 750 miles, though, and the authors suggest that’s part of the reason why these long-haul routes have large negative operating balances. They recommend that the PRIIA reauthorization require state operating support for long-haul routes (as well as giving states greater flexibility and dedicated funding and accelerating completion of a National Rail Plan).

State contributions to rail lines aren’t just important because they decrease net losses. “Importantly, once they have “skin in the game,” states are motivated to target investments more precisely and develop plans more comprehensively, better tailoring maintenance needs and capital improvements to local demands,” explains Puentes in a blog post.

The report authors are clear that “‘profitability’ for Amtrak is not in and of itself the primary goal” — after all, governments give big highway grants and offer tax incentives for airlines. And “geographic equity” is a perfectly reasonable goal for long-haul passenger rail routes. Still, the authors recommend that if states can’t agree on the importance of such routes, they should be scaled back.

PRIIA will presumably be reauthorized for another five years. In that time we’ll probably see even more growth in ridership in the corridors that already account for the majority of Amtrak ridership, and perhaps less of a gap between expenses and revenue on long-haul routes. What I hope national and state rail plans will address is the possibility that auto and air travel might become less attractive compared to passenger rail. Maybe we’ll decide to address the deficit by eliminating fossil-fuel subsidies or adopting a carbon tax (I can dream, right?), or maybe airline mergers or constrained oil supplies will make plane tickets far more expensive than they are today. In such a future, even those who call for slashing federal subsidies to Amtrak might be glad to have the option of taking the train.

Update, 3/15/13: The New York Times Magazine has printed an excerpt of this post on their Letters page, so I thought it might be a good time to spell out the public health benefits of public transportation.