Yesterday, as part of a big infrastructure speech, Rahm Emanuel announced not only that he was still pursuing his dream of a devoted O'Hare express train to downtown, he'd made a new hire to get the deal done and set a three-year goal to "start" the project. Sounds like a big deal—and the city's already committed up to two million on a study for the project.

It's not the first study to be done, nor the first time this project has been pushed. When I started at the Chicago Reader over a decade ago, Ben Joravsky wrote a piece titled, "How Much Would You Pay to Get to the Airport 15 Minutes Faster?: The City Council just approved a plan to spend $213 million on a station for new train lines nobody asked for and nobody can afford to build."

That was in 2005. The Daley administration started building that station soon thereafter and subsequently abandoned it in 2008. (Greg Hinz got an interesting tour of it, if you're so inclined.) So we have previously committed far more money and time to the idea and seen fit to drop it.

Last year, when the city signed the contract for the express-train study, Daniel Kay Hertz made four arguments against it for Chicago. No. 1 was the failure of Toronto's Union Pearson Express, which was then attracting just over 2,000 riders a day, less than half of what they deemed a successful ridership figure and less than a third of what it would take to break even—not typically the point of public transit, which is expected to be subsidized as a general good, but a harder case to make for an expensive ride catering to business travelers. Since then daily ridership has gone up to over 7,000, but only after cutting the one-way fare from $27.50 to $12 ($19 to $9 with a card), much less than the $25 to $40 figure that's been suggested for the O'Hare Express.

The Heathrow Express is the gold standard of dedicated airport express trains: privately financed, profitable, and popular. If Chicago is going to keep to its no-public-money goal, it's the ideal. But the Heathrow Express's 15-minute journey saves up to 45 minutes and costs about half as much (£25 versus £45-70) compared to grabbing a taxi in London. An express train from O'Hare to downtown could save a lot of time under the worst conditions (25 to 30 minutes versus 1 hour and 15 minutes) but wouldn't save much time under more typical conditions. The cost savings would be closer to a quarter or a third ($25-$40 versus $30-$40 on average plus tip). The value proposition for private money is a bit trickier.

Why not just tell people to take the Blue Line—which has much shorter headways than any express train will ever have, and is maybe 15-20 minutes longer, meaning that overall it's basically just as efficient—as many have suggested? This is the other major piece of the issue. When Richard M. Daley was a brand-new mayor in 1990, the CTA did a study of transportation to O'Hare, finding that only about five or six percent of people got to O'Hare via the Blue Line, compared to about 20-25 percent by taxi/limousine. It was even lower than hotel vans.

"In general," they concluded, "the common tendency for more affluent travelers to regard public transit as a 'lesser' mode, intended more for the general population but not necessarily for them, probably represents a major psychological barrier in the marketing of transit connections to the Chicago Loop." That's changed a bit; when the CTA studied the express-train idea in 2006, they found that residents used the CTA about 20 percent of the time, and business travelers about 11 percent of the time, but both are still lower than taxi use.

If Blue Line use has improved over time, why push for an express train? A master's student at MIT, Julia Nickel, wrote her thesis on the subject, and concluded that the Heathrow Express "signaled London's competitiveness as a global city," and that "the recent plans at Paris, Munich, and Chicago seem to be motivated by a perceived need to signal global competitiveness."

She was probably on to something. Here's what Emanuel said yesterday: "If London and Hong Kong, Tokyo, and Toronto can offer this service, the city of Chicago can and must also offer it."

Of course, London got private businesses to signal its competitiveness as a global city. If Chicago can't, that's a lot of money to pay for a signal.