What the Bus? I Thought Trains Were The Greenest Transit Mode?
Dear EarthTalk: I always assumed the train was the greenest form of mass transit, but a friend told me I would be better off taking the bus. Could this be true?
—Jane McNeil, New York, NY
Most of us assume that train travel—whether for getting around town, commuting to work or for long hauls—is the most eco-friendly mass transit “mode.” Indeed, trains seem greener, with some relying exclusively on electricity while others utilize a single diesel-powered locomotive to pull dozens of passenger cars.
But even though trains are no slouch when it comes to fuel efficiency, buses, even though they spew diesel exhaust and get only about six miles per gallon, may be even better.
“The reason … is that they are usually full of people, giving [buses] the highest miles per gallon per passenger, at 208,” reports CNN’s Steve Hargreaves based on his research digging into Department of Energy data. He adds that trains are the next best choice for the eco-conscious traveler, whether commuting or doing a longer haul. “A city train (think subway or light rail) gets 52 mpg per passenger (or the equivalent, if it’s electric), while a commuter train—usually used to connect the suburbs to a city—gets about 44 mpg per passenger.”
A landmark 2013 study in Environmental Science and Technology by researchers at the International Institute for Applied Systems Analysis (IIASA) and the Center for International Climate and Environmental Research (CICERO) backs up these findings. The researchers found that bus travel noses out rail travel in fuel efficiency and carbon impact on typical business or holiday trips ranging from 500-1000 kilometers (300-600 miles), generating only about 20 percent of the per passenger emissions as driving alone in a typical gas-powered car.
“Motor coaches leave carbon in the dust,” reports the non-profit Union of Concerned Scientists (UCS), adding that a couple can cut their travel carbon emissions in half by boarding a motor coach instead of taking their Prius. “And if they take the motor coach rather than flying, they will cut their emissions by 55 to 75 percent, depending on the distance they travel.” And given that many bus companies have ditched their old buses in favor or new models replete with not only more efficient engines but also reclining seats, on-board entertainment and WIFI, the bus could become your new favorite way to travel.
Though buses are the current green leader, trains are catching up fast. All of Amtrak’s trains in its busiest Northeast Corridor now eschew the old diesel generators that used to power their locomotives, and run instead on an increasingly renewable supply of electricity. Some $10 billion in investment in high-speed rail by the Obama administration means trains are getting more efficient across the country as well.
While Candidate Trump promised he would pour hundreds of millions of dollars into further boosting high-speed rail infrastructure, his 2018 budget does more to decimate Obama’s progress on the issue than augment it. Whether he will follow through with a plan to further bolster U.S. rail travel remains to be seen. In the meantime, while trains remain a viable green choice, choosing Greyhound over Amtrak might be the better option for the time being.
01/06/2018 @ 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.
01/06/2018 @ 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.