Monday, January 5, 2009

Public Transportation and Energy Efficiency

Reconsidering the issue of how the world might cope with the contraction of oil supplies in the next two decades, I found myself thinking about the issue of public transport. It is often said that a trip on mass transit uses only half as much oil as a trip by car, and equally often, we see such figures challenged.

One set of numbers that has attracted attention is the Department of Energy's calculation in the Transportation Energy Data Book (specifically, Table 2.12 of the Data Book's 27th edition) that countrywide buses may actually use more British Thermal Units than trucks when measured on a passenger-mile basis, 4200 BTUs per passenger-mile compared with a bit under 4,000 for trucks, and 3,500 for cars.

The Data Book's authors are careful to warn readers against simplistic comparisons between one mode and another, and it is right to do so. Given that many more of those car-miles than bus-miles are on the highway, where vehicles generally get better mileage, it would seem that the above comparison is slanted in favor of cars and trucks. The mile-counting also fails to capture the fact that bus trips are much less likely to be door to door than car trips, their passengers walking a stretch of the distance uncounted in the above analysis (though one has to wonder whether that fully compensates for the extra distances traveled on the more convoluted bus routes). And bus drivers do not circle around endlessly looking for parking spots the way car drivers do, adding unnecessarily to their total mileage.

It is also worth noting that the use of BTUs overlooks important differences in energy forms, overall energy use and oil use two different matters. Buses generally run on diesel, not gasoline, which is about a third more efficient, and studies which look at the difference in oil use (and in particular, the gasoline that would have been used in the absence of public transport, like ICF International's Public Transportation and Petroleum Savings in the U.S.: Reducing Dependence on Oil) tend to produce a more favorable picture of public transport's impact. And despite all its problems, the rail component of American public transport is still more efficient than private car use (while having the additional virtue of being able to operate on electricity), so that when mass transit is taken as a whole, it does not fare so poorly.

The fact that studies in other countries often post better numbers is not irrelevant. Low ridership in the U.S. is a factor in this study (the Data Book assumes 8.8 passengers on a bus, on average, make of that what you will), but this goes only so far in explaining the issue. The Public Transport Users Association of Victoria, Australia, cites Australian Greenhouse Office figures showing that even lightly loaded buses (carrying just 10 passengers, only slightly more than in the American case) are three times as energy-efficient as private cars. (Indeed, one has to wonder what a more detailed examination would produce, and in particular, how New York and Boston stack up against the Sun Belt sprawl of Atlanta, Dallas, Los Angeles or Miami-where visiting New Yorkers are more than willing to lecture locals on the comparative shabbiness of their city's service.)

Additionally, when the energy cost of manufacturing cars, as opposed to buses and trains, is counted in, the resulting figures strongly favor the latter. The same may go for the public infrastructure necessary to support them, one assessment positing that public transport consumes just 1/16th as much infrastructure. Given the energy costs of so much construction, and the fact that asphalt production is itself a major oil consumer, this too holds out the prospect of considerable potential savings through greater investment in this area.

In the end, the data would seem to validate the claims for public transport's greater energy efficiency, and especially its oil efficiency. And assuming that the much-discussed stimulus package actually materializes, doesn't get whittled down to nearly nothing, and ends up actually containing a substantial component of infrastructure spending (none of these things is certain, and the last has a tendency to be overhyped, as seems to have been the case in Japan's stimulus packages during the 1990s), then mass transit will be an especially worthy area for such spending.

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