Unsurprisingly, given my demographic, this image is getting a lot of play in my Facebook feed. And as the daughter and wife of train obsessives, I admit, my heart feels a little tug. How cool would it be to take a high-speed train from New York to Los Angeles?

Cool. Very cool. But not cool enough to happen.

The longest high speed rail line in the world runs from Guangzhou to Beijing, a distance of about 1300 miles which the train covers in 8 hours. That's less than half the distance from New York to LA by the most efficient route, which will be even longer after it's done running through Cleveland, Omaha, Denver and so forth. 18 hours on a train is too long for anyone to take it, unless you put in sleeping cars, which would cut down on the carrying capacity of the train. And the intermediate routes--Chicago to Omaha, say--are unlikely to support even the operating costs, much less the massive capital investment required to install the train tracks between those cities.

Transcontinental rail was a great idea in the 19th century, when it was actually the fastest way to get from point A to Point B. But in the modern world, where there is competition from alternative modes that are either faster (air) or cheaper and more convenient (autos), such a project could never get the ridership needed to make financial sense.

But what about environmental sense, you may ask? Couldn't high speed rail displace more polluting forms of transportation and relieve road congestion?

Sort of yes, but the effects are likely to be more modest than you think.

High speed rail is not necessarily particularly efficient. The energy required to move a train that fast means that for a given number of passengers, the CO2 emissions are higher per passenger mile than they are for conventional rail. The benefit comes from luring additional passengers onto the train with the promise of a faster journey.

But for this to work, the passengers have to be there--and they aren't on the Omaha to Denver route. Nor Las Vegas to Chicago. Not in the numbers that would be needed to support a truly transcontinental rail route, one that ran, at a minimum, six to eight times a day.

Without that kind of passenger traffic, it would never make sense to lay the tracks (new tracks are required because for high speed rail to be truly high speed, it needs very, very straight tracks.) The Chinese government has a variety of strongarm measures to simply take the land it wants (not to mention a lot of low-productivity farmland). The US government has to tediously assemble plots one by one, compensating the folks whose land it has seized, and then jumping through various obstacle courses comprised of local and environmetnal review processes.

So we aren't getting a national high speed rail network. Your wallet should be glad. But those of you who would really like to hurtle across the American landscape at 300 mph from Chicago to Las Vegas are permitted a small sigh.