As big-time blogger Duncan Black noted over the weekend, high gasoline prices seem to have boosted ridership on some of the the nation’s transit systems — which led big-time blogger Matthew Yglesias to speculate that gas consumption may be more sensitive to price than economists have predicted.

Yglesias’ take seems mistaken to me. Nationwide, less than 5 percent of all commuting trips are taken on transit; and commutes represent a minority of all trips that people make, but a fairly large share of all transit trips taken. So even if transit ridership were boosted by, say, 20 percent — which is a huge spike indeed — that might represent a decrease in vehicle trips of, oh, a half a percent or so at most.

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In fact, it seems to me that any recent increases in transit ridership are pretty much in line with what economists would predict from recent gas price increases. (See here, especially table 8, for a summary of economic predictions for the relationship between fuel prices and demand.) Of course, that doesn’t necessarily undermine Yglesias’ main point, which is that higher gas taxes would decrease fuel consumption. I’ve also got to second this part of Duncan Black’s response to Yglesias:

[L]and use patterns in much of the country have made it quite difficult for any proposed transit systems to really improve the lot of most existing homeowners/commuters. Expanding rail systems into existing suburban areas really only makes … sense if it’s accompanied by some land use changes in those areas (there at least needs to be higher-density development around the stations themselves).

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As far as I can tell, this is just about right: transit is rarely cost-competitive in low-density, sprawling neighborhoods, since both riders and destinations are simply too spread out. (Color me extremely skeptical about supply-side theories of transit ridership.) Which means that, since the shape of our cities changes much slower than gas prices, a lot of us may be stuck in our cars no matter what gas prices do in the short term.