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  1. miltonhanzel
    January 6, 2018 @ 2:31 pm

    Thanks for tackling this complex issue. I am writing to increase the complexity, as I think you missed the mark with this article.
    I don’t argue the point that trains with empty seats are less efficient than full buses, so you are quite correct in the short term.
    In the long term view, however, we note that trains are only less efficient until they achieve ridership goals. This period of reduced efficiency is an infrastructure investment: just as rail must be installed, so must ridership be grown.
    To the extent that consumer choice influences industry priorities, choosing the train will shift ridership from bus to rail. Looking at the simple statistic of mpg/passenger is unhelpful, in this case, as we need to get the trains full.
    This article pushes people in the opposite direction, sadly.


  2. Michael Ash
    January 6, 2018 @ 5:37 pm

    Thank you very much for addressing the important issue of the energy efficiency and emissions intensity of alternative modes of transport in https://earthtalk.org/train-or-bus/. I read your column regularly in the Daily Hampshire Gazette (Massachusetts).

    I write to express three concerns about the piece:

    1. The unit of measurement from the CNN report, “miles per gallon per passenger,” is incorrect or, at best nonstandard and ambiguous (if the unit is read as miles / (gallon / passenger)). It’s simply not clear what “52 mpg per passenger” means. A more appropriate unit of measurement is passenger-miles per gallon. This measures that so many people were moved so many miles per gallon of fuel expended. Experts in the field typically invert this term to gallons per passenger-mile and then report BTU per passenger mile (converting gallons of petroleum to their energy content in BTU). The inverted terms, Gallons per passenger-mile or BTU per passenger-mile, are *bads*, not *goods*. Hence, lower BTU per passenger-mile indicate a more efficient mode of transit.

    2. According to Table 2.14 “Passenger Travel and Energy Use, 2015” of Chapter 2 “Energy” of the 2017 Transportation Data Book http://cta.ornl.gov/data/index.shtml, rail is substantially more energy efficient (lower BTU per passenger-mile) than buses. The article that you cite http://pubs.acs.org.silk.library.umass.edu/doi/ipdf/10.1021/es4003718 does show trains and buses as close with buses slightly better in terms of grams of carbon dioxide per passenger-mile (which like BTU per passenger mile is better if lower). The IIASA/CICERO results are sensitive to assumptions about occupancy. I’m not an expert on transport energy efficiency and I’d like you to provide more expert analysis.

    3. The piece does not distinguish between marginal and average energy efficiency. Adding an additional passenger to a train is essentially free; there is virtually no additional energy use when one more passenger rides. That’s less true for buses. It’s not true at all for car trips. (Car pooling on an already planned route is, however, better than riding alone.) So probably for planning a trip for maximum efficiency hopping on a train is the most efficient way to travel.

    In conclusion, you are absolutely correct that trains or buses beat cars badly in terms of energy efficiency and climate impact. I’m not sure you have accurately characterized trains vs. buses. But so much better are trains or buses that it’s certainly better to take whichever is more comfortable and convenient than to take a car.

    Thank you very much for tackling this issue and thanks for your consideration.


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