I've done some more thinking about the Glaser and Kahn paper I blogged about the other day. (Update: The cite to the full paper is The Greenness of Cities: Carbon Dioxide Emissions and Urban Development August 2008 NBER Working Paper #14238 www.nber.org.) Glaeser and Kahn examine total energy use among major metropolitan areas in order to compare carbon emissions among cities. But their data also allow us to compare gasoline use city by city. That's just as interesting a comparison, at least to me.
Glaser and Kahn even allow us to make an apples-to-apples comparison because they have constructed a composite "median" household for each city to use as their points of reference. For example, they don't use per capita gasoline consumption as their point of comparison. They instead estimate the expected gasoline consumption of a hypothetical $62,000/year household with 2.62 members for each city, using survey data and (I assume) some fancy statistical techniques.
They report pounds of carbon emitted rather than gallons of gasoline consumed, but since they tell us how much carbon they assume one gallon emits (23.47 pounds), we can easily convert their data into gallons.
Here is the relevant table from their paper:
Here is a chart I compiled from their data depicting relative gasoline consumption:
The thing that struck me when I looked at the numbers was the relatively small difference in gasoline consumption between Houston and most other cities. (Third column.) Glaser and Kahn's hypothetical $62,000/year household uses only 55 more gallons per year in Houston than in D.C. It uses only 135 gallons more gallons per year than the corresponding San Francisco household. The Houston-Chicago gap is only 118 gallons per year.
The gap between Houston and old-line northeastern cities (particularly New York) is larger, but is largely offset by their greater consumption of heating oil. (Remember Hugo Chavez offering free heating oil to Boston's poor?)
This chart makes the point better:
There is no question that steep gas price hikes would hurt Houston (or Dallas or Austin) households. At $3/gallon, the Houston household is already spending 5.4% of its gross income on gasoline. At $4/gallon, it would have to spend 7.2% of gross income on gasoline, assuming no change in gasoline consumption. But the San Francisco household is spending 4.8% of its gross income on gasoline, a figure that would rise to 6.4% with a $1 increase in the price of gasoline. That 0.8% difference is smaller than I expected.
Glaser and Kahn also compare city and suburban gasoline use:
I summarize the corresponding gasoline consumption numbers in columns 5 and 6 of my chart, and compare suburban Houston households with central city residents elsewhere in column 7. No surprise that the gap grows significantly. But it is possible that, given their much higher housing costs, central city residents may be even more susceptible to price variations in commodities like gasoline. Those suburban Houston households pay a lot less per square foot of housing than similarly situated households in LA, San Francisco or DC.
These simple charts don't tell the whole story, of course. Gasoline consumption is not completely inelastic, especially over the long run. One could argue that because residents of central cities have access to better mass transit, it is easier for them to substitute away from gasoline use, making their demand for gasoline more elastic than suburb dwellers. Put simply, city dwellers can cut down on their driving more easily than suburbanites.
That's certainly plausible. However, city dweller's access to better transit is already reflected in their lower gasoline consumption. They've already picked the low-hanging fruit, so to speak. The barrier to additional transit use is often not the difference in monetary cost, but the difference in time and convenience costs.
Of course, there is some price at which drivers will begin to substitute to mass transit wholesale. But the suburban drivers have options, too. A Houston suburbanite who switched to riding the bus or carpooling would save (on average) more gasoline per commute than a central city resident. Likewise, a Houston suburbanite who combined two errands would save (on average) more gasoline per errand.
This is ultimately an empirical question. Like everyone else, I think gas prices are headed up, at least over the next few years. It will be interesting to see the relative adjustments made by Houston drivers and those in the more compact northeastern and western cities.
Relative elasticities aside, the numbers are still interesting, especially the aggregate metropolitan area data. I never would have guessed that a "typical" metropolitan Houston household uses only 5 more gallons per month than its metropolitan D.C. counterpart.
One final point. There is one area where western and northeastern cities wipe the floor with us, the denizens of the hellishly hot places: Electricity. We use fiendish amounts of the stuff. (There's archaeological evidence that Austin was inhabited before the invention of air conditioning, but some scholars dispute its conclusiveness.) If electricity prices shoot up like gas prices, we will suffer a lot more than our friends out west and up north, and there'll be nothing we can do about it.
