Is green U.S. mass transit a big myth?

Wednesday, July 30th, 2008

Is green U.S. mass transit a big myth? Yes, Brad Templeton discovers, after pulling numbers from the U.S. government bureau of transportation statistics and the Dept. of Energy Transportation Energy Data Book (especially table 2-12).

USA Transportation Energy Use
BTUs per passenger-mile

How can this be?

A full bus or trainload of people is more efficient than private cars, sometimes quite a bit more so. But transit systems never consist of nothing but full vehicles. They run most of their day with light loads. The above calculations came from figures citing the average city bus holding 9 passengers, and the average train (light or heavy) holds 22. If that seems low, remember that every packed train at rush hour tends to mean a near empty train returning down the track.

Transit vehicles also tend to stop and start a lot, which eats a lot of energy, even with regenerative braking. And most transit vehicles are just plain heavy, and not very aerodynamic. Indeed, you’ll see tables in the DoE reports that show that over the past 30 years, private cars have gotten 30% more efficient, while buses have gotten 60% less efficient and trains about 25% worse. The market and government regulations have driven efforts to make cars more efficient, while transit vehicles have actually worsened.

In order to get people to ride transit, you must offer frequent service, all day long. They want to know they have the freedom to leave at different times. But that means emptier vehicles outside of rush hour. You’ve all seen those huge empty vehicles go by, you just haven’t thought of how anti-green they were. It would be better if off-hours transit was done by much smaller vehicles, but that implies too much capital cost — no transit agency will buy enough equipment for peak times and then buy a second set of equipment for light demand periods.

Transit planning is also driven by different economies. Often transit infrastructure (including vehicles) is paid for by state or federal money, while drivers (but also fuel) are paid from local city budgets. This seems to push local city transit agencies to get bigger vehicles and fewer drivers where they can, since drivers tend to be hired full-time and can’t be kept idling in low-demand periods.

In Templeton’s opinion, you should still take transit, because the marginal energy cost of one more transit passenger is much less than the energy cost of one more car, even if the average cost is no lower.

In fact, because transit systems have high fixed costs and low variable costs, they need high ridership to make sense, which has led to massive subsidies to reduce prices:

Transit fares are highly subsidized. It’s not uncommon for a $1.50 transit ticket to offer a ride that costs the agency 3-4 times as much to provide. (In U.S. big cities, on average subsidies pay for 44% of rail cost and 69% of bus cost. Suburban buses can see almost 90%.) Cars are also subsidized of course, via roads (which also provide subsidy to buses, trucks and street cars, of course) and via free parking and forced parking construction requirements. To the extent that roads are funded by gasoline taxes — which varies from place to place — this is not a subsidy so much as a user fee.

Anyway, Templeton also provides his numbers in MPG-equivalents.

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