In discussions about about high gas prices, global warming, etc., it is not uncommon to hear someone say that what we really need to put more money into public transit, as this will help energy conservation. But as the above chart shows, more public transit may not actually save us all that much energy. If, that is, it saves us any at all.
How can light rail end up being less energy efficient than cars? The answer, as explained by Brad Templeton, has to do with the occupancy rate:
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.
The numbers involving light rail are so stark that they’ve led the blogger Warren Meyer to offer a standing bet for new light rail systems:
I bet that for the amount the system cost to build, every single daily rider could have instead been given a Prius to drive for the same money; and, with the operating losses and/or subsidy the system requires each year, every one of those Prius drivers could be given enough gas to make their daily commute. And still have money left over.
I can only speak for myself, but I ain’t betting.
UPDATE: Katerina offers a well reasoned an informed response here.
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