Hey Mr. Green,
What of the recent claim that trains can be as hard on the environment as airplanes?
--Mark in Richmond, California
Yes, they "can," but remember that the operative word is "can," not "are," because not all trains are created equal. Some best planes environmentally, and some don't. But a bad rap on trains may be spreading because of some rather superficial interpretations of recent transit research. So let's try to get the facts straight before right-wing pundits start whipping up anti-train sentiment by twisting the truth -- like they already have been by dissing everything from hybrid cars to fluorescent bulbs to bicycles.
So it all depends on the kind of train, what type of infrastructure is built to support it, where it's located, what kind of energy it runs on, and how many passengers ride. It seems fairly obvious that if a train has few riders, it may well be burning more fuel per "passenger mile" and spewing out more pollution per mile than a packed airplane. Conversely, it may emit less per passenger if it's jam-packed.
But comparing methods of travel gets a lot more complicated when you go beyond engine energy and look at the total environmental impact of everything from obtaining all the raw materials needed to manufacture everything involved, and to build and maintain roads, rails, and airports. Such variables were recently analyzed in an astonishing doctoral dissertation by Mikhail V. Chester at the University of California, Berkeley. No wonder this document and an article by Chester and his dissertation director Arpad Horvath have attracted attention to the train/plane question. What these guys do is go way beyond comparing energy use and greenhouse gases from vehicles themselves, and look at the energy and pollutants (like sulfur dioxide, nitrous oxide, and carbon monoxide) generated by processes from the entire life cycle of planes, trains, and cars and the infrastructures that support them. Chester even researches the impact of maintaining insurance on the various modes of motion!What we get from this comprehensive life cycle analysis is what's indicated above. For example, the San Francisco Bay Area's electric train-transit system known as BART is responsible for substantially less carbon dioxide and nitrous oxide emissions per passenger mile than any plane. But Boston's Green Line light rail is responsible for slightly more carbon dioxide than midsize and large aircraft, but way less nitrous oxide. Yet it almost bumps the top of the chart on sulfur dioxide emissions. If Boston were less dependent on fossil fuels, the numbers would look very different. In fact, as these researchers point out, all comparisons can change drastically if energy sources, technologies, and demographics change.
You'll notice that I mentioned they also compare cars to other modes of transportation. Because of this, it seems to me that people who dwell on the train/plane issue have got the whole thing upside down. In almost every category, planes and trains are far better for the environment than individual passenger vehicles. San Francisco's BART accounts for less than half as much carbon dioxide per passenger mile as an SUV. But remember, we're talking "per passenger mile" throughout. If more people only had the good sense and social grace to carpool, motor vehicles would be far less ruinous.
All this should warn us not to use data perversely. A comparison of San Francisco's commuter train with a large jet doesn't mean all that much, because nobody is flying on the morning commute, though Steve Jobs once reportedly used a helicopter. But the fact that a commuter train, whether Boston's or San Francisco's is so much better than a car, makes it the best option for such areas. What's most useful about this kind of research is that it helps us view a system holistically. Yes, that a train might not be the ideal solution, and, yes, it could be a boondoggle in the name of environment if it doesn’t have enough riders or requires intense construction efforts or is too dependent on fossil-fuel energy.
Finally, there's your basic geography. Long commutes and trips to the mall from oversized houses out in the sprawl create environmental dilemmas no matter what the mode of transportation. After all, New York City's carbon footprint is only a third of the national average, thanks to its compactness, transit system, and apartments that average half the size of new houses in the suburbs. A ban on building in the middle of nowhere might be more important than the transportation we choose to get to and from it.