In transit : The energy inefficiency of light rail

In transit : The energy inefficiency of light rail

If you quizzed the general public about what modes of transportation were the most energy efficient, you'd likely get back an answer mentioning rail lines or trains. But the idea that rail lines are the most efficient way of getting people from place to place is an urban myth. The truth is that a variety of factors make rail energy inefficient when compared with other modes of transportation.

At first this idea might seem surprising. In terms of basic physics, steel wheels on steel rails face much less friction than do tires on pavement. And one might think that electric rail cars have an efficiency advantage over ordinary buses that burn fossil fuel. But the physics of the situation actually favors vehicular traffic: Rail cars tend to be heavier per passenger than buses. That even goes for light rail. A light-rail car weighs about four times as much as a typical bus, but carries only about 2.5-times the load.

These noteworthy facts come courtesy of Randal O'Toole, a public policy analyst who writes frequently about light rail. O'Toole has a lot of detractors among urban planners because he says that rail lines make sense only in densely populated areas where they run at near capacity much of the time. Regardless of what one might think of his stance on the practicality of mass transit, he makes interesting points about the energy efficiency of various forms of travel.

Using DoE data, he points out that since 1970 the fuel economy of the average passenger car has improved by more than 40%. Average vehicle occupancy rates have declined since then, so the effective improvement in BTU/passenger mile is only about 28%. In contrast, most other forms of transit have become less efficient since 1970 when measured this way. Buses were the worst performers because transit agencies have tended to buy air-conditioned buses too large for what passenger traffic has really required. Energy efficiency of rail lines suffered over that period because municipalities have increasingly built them in areas of low population density where they carried relatively few passengers.

The steadily rising energy efficiency of automotive traffic should be a consideration for future rail projects, O'Toole points out. To figure out whether a new rail line will be more energy-efficient than autos, one must determine whether the rail line will be more efficient than the future autos on the road when it is complete. Rail lines take about ten years to construct and have an operational life of about 30 years. So if a rail project is to save energy, it must be more efficient than the average auto on the road 20 years from now.

And interestingly enough, only transit systems in roughly eight of the nation's most urbanized areas consume a lot less energy than the 3,700 BTU/passenger mile that cars now average, according to 2006 statistics from the Federal Transit Administration's National Transit Database. The most energy-efficient system is in Honolulu and it just operates buses. Only it and the NYC system consume less than the 2,660 BTU/passenger mile that autos are expected to use in 2030.

These statistics are good to keep in mind if you are ever in a position to make decisions about the most efficient means of moving people from one place to another.

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