Forgive me for talking about high speed rail even though Ryan Avent says I'm not allowed to. I just can't control myself, I'm afraid.
As libertarians go, I'm a big fan of high-speed rail. I think it would be very nice if we had some in the Northeastern United States, where it might actually work, rather than the pathetic Acela that shaves a whole fifteen minutes off the trip between DC and New York. Unfortunately, that is apparently never going to happen, because in the United States, acquiring new rail rights-of-way seems to be virtually impossible. That means that the Acela has to run on existing track, which is not very good for high speed rail because, first, it was not designed for a train that accelerates to hundreds of mph, and second, there are other trains on it that don't go hundreds of mph, which slows everything down.
So we're not going to get true high speed rail in one of the two areas of the country where it stands a decent chance of working. Instead, we're going to get high speed rail in between Dallas and Houston or some other likely location--at least if the HSR part of the stimulus actually has its intended effect.
Ryan Avent defends these sorts of rail links on the grounds that if you view intercity rail as a substitute for air travel rather than car travel, they make sense. And I think that's fair. But I think that Avent underestimates the difficulties in doing this. The northeast corridor is the only place where people use trains as a substitute for cars for relatively short distances (sub 4-5 hours), because you don't need a car when you get there--and also, because road congestion makes car travel dicey, schedule-wise. This generally isn't much of a problem in flyover country.
Ah, but what about all the people who do fly between Houston and Dallas? Surely they might be persuaded to take a train if it existed?
Maybe. But I think there are a number of problems with this. First of all, many of the people flying between Dallas and Houston are not actually ending up in those cities; they're going somewhere else, because Dallas is a major hub. When I want to fly up to see my family in upstate New York, I don't take Amtrak to Penn Station and then trek out to LaGuardia, even though I much prefer rail travel to air travel. So high speed rail doesn't readily substitute for air travel unless you have a lot of connections running out of Dallas. I don't think it's an accident that the two places in America where rail kind of works--the northeast corridor, and the LA-San Diego route--are coastal runs where the regional links run down a basically straight line. And the reason that they are conveniently in a straight line is that both regions happen to be sandwiched on a narrow strip between the coastline and a big mountain range that limited inland development during the formative years. In the middle of the country, where you need to add an east-west axis to your planning, things rapidly get more expensive.
The other reason I don't think that rail is going to compete with air in most places is the very thing that makes air travel so environmentally problematic: frequency of service. For high speed rail--or any sort of rail, really--to be an environmental boon, the trains have to run pretty full.
During peak times, by my count a flight leaves Dallas for Houston every half hour, the better to allow people to tailor their flights to their schedule and their connections. But most of these flights are tiny regional jets that carry perhaps 60 passengers when full. An Acela, by contrast, carries 300. If every single one of those planes was full, and every single one of the passengers switched to rail, you'd have a peak schedule of once every hour and a half to run the train at 80% capacity. But of course, those planes aren't all full, and not all of the passengers will switch to rail, because as I mentioned above, many of them are connecting to other flights.
Maybe you could put the train station in the airport, but that doesn't encourage dense urban development, and also, even then I doubt people would use it. Once you have to clear security, you're going to fly, because for all but the shortest trips, it's faster.