THE FORTY YEAR BRAIN DRAIN. Trains for America invites readers to giggle at some high-speed-rail-skepticism from The Detroit News (motto: all the news that's fit to deliver on Wednesday and Saturday).

No matter where the high-speed rail is eventually located, the concern is that taxpayers will never see the end of their transit investment. Mass transit systems never pay for themselves.

Well, fine. I was surprised to find so many gravel or unimproved roads not too far from Detroit. It must be that the Infrastructure Fairy never got around to paving them, or perhaps she, like just about everybody else in Michigan who had any ambition, went someplace else.

The serious point: some infrastructure projects, including transportation systems, pay for themselves indirectly, by making possible sufficient economic activity that people bear the taxes.

Perhaps there's no point in building a high-speed line to Detroit, as there are going to be fewer people wanting to travel there. And perhaps a high-speed line to Grand Rapids is a regressive transfer, catering to parvenu Chicagoans with lakefront property in Harbor Country. (The old money is in Door County, on the windward shore of Lake Michigan.)

If the Hotelling Principle of exhaustible resources has any effect though, some alternatives to driving make sense.

The rapid increase in oil prices last year directly contributed to the economic downturn by gutting the disposable income of households around America. This might not have been hugely problematic, had households been able to continue borrowing to pay for consumption, but in combination with the credit crunch the effect was deadly. It was deadly, note, because Americans were not able to rapidly and easily substitute away from driving, thanks to the country’s settlement patterns and inattention to transit.

Meanwhile, the decline in gasoline prices that has taken place since July has been a major source of economic stimulus. Had prices not fallen so dramatically, consumption would have fallen by considerably more. Still worse, authorities might have been more reluctant to use fiscal and monetary stimulus, given the threat of ongoing inflation.

But this is a temporary respite. It’s worth pointing out that the most significant collapse in global economic activity since World War II barely managed to push oil into the $30 per barrel range. Even now, as economic outlooks remain dim, prices have edged back up into the neighborhood of $50 per barrel. Given the collapse in new exploration and investment that has accompanied the drop in oil prices, one doesn’t have to be a genius to predict the path of oil prices once recovery begins. And the rise in oil prices will be a drag on growth.

That drag will affect railroads, including electrified ones. The Principle of Substitutes is one of those economic laws of conservation that contribute to our reputation as the dismal science.