Saving the Planet by Flying

The Guardian reported yesterday about people who think they are saving the planet by giving up flying and taking the train instead. They should think again, especially for those who are Americans.

According to the 2016 edition of the Transportation Energy Data Book, Amtrak in 2014 used an average of 2,186 British thermal units (BTUs) per passenger mile in 2014, while the airlines used 2,511. Jet fuel and Diesel fuel both have about the same BTUs and produce about the same greenhouse gases per gallon, so that would seem to give rail travel an edge.

But airplanes don’t have to go around mountains or follow meandering river valleys to get to their destinations. The Amtrak route from Portland to Washington DC is 3,035 miles long, while airlines only have to go 2,350 miles. Multiply through, and the Amtrak trip used 6.6 million BTUs while the airline flight used only 5.9 million.

Moreover, the Amtrak number is an average for all Amtrak trains. Long-distance trains (the kind the people in the Guardian were using) weigh more per seat and often fill a smaller percentage of seats than short-distance trains.

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Many of the long-distance trains also fill a smaller percentage of seats. According to Amtrak’s 2018 performance report, the Acela filled an average of 61 percent of its seats, and the Northeast Regionals 57 percent. The Empire Builder filled only 54 percent of its seats, further reducing its energy efficiency.

You may have noted that I cited the 2016 Transportation Energy Data Book even though there have been two editions since then. That’s because, as I’ve noted here before, the authors of the two most recent editions decided not to count the generation and transmission losses of electric energy when measuring the energy used by electric trains. It takes 3,000 BTUs of energy to deliver 1,000 BTUs of electricity to the railhead, and in the Northeast Corridor most of that energy comes from burning fossil fuels. So, when they eliminated that, it greatly reduced Amtrak’s apparent energy consumption. Internal combustion engines lose about two-thirds of the energy of their fuel in heat, while electric engines lose about two-thirds in generation and transmission losses, so in reality both kinds of trains require about the same BTUs per passenger mile.

Airplanes use most of their fuel in taking off and landing, so flying may not look as favorable for short trips as trains. The results may also differ in other countries, where trains may be lighter or fill more seats. However, in any of these cases, the differences in emissions between flying and taking the train are likely to be small. Anyone who is planning an airline trip shouldn’t feel guilty about greenhouse gases; anyone who thinks that taking a train is saving the planet is fooling themselves.