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Are Trains or Buses Better for the Environment?

America loves its cars and planes, but they are huge contributors of carbon to the atmosphere. What is the cleanest form of transit available?

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America's massive highway system provides a low-cost foundation for scaling up intercity bus service, which makes this form of transit more green than trains, say advocates.
(Shutterstock)
The omicron wave of the pandemic is ebbing, and Americans are itching to get out of their homes. After a holiday season marred by COVID-19 outbreaks, virus fears and canceled trips travelers are making moves again. For the climate-conscious among the traveling class, however, a question looms: What is the greenest way to get around?

There are obvious answers, which can be dispensed with right off the top. Plane travel is apocalyptically bad for the environment and car travel isn’t any better, largely because it is so inefficient. Personal vehicles account for almost a fifth of American carbon emissions.

Now that we’re all feeling nice and guilty, let’s consider the alternatives. The most carbon-free means of travel are, of course, the least practical for long excursions.

“If your personal objective is to reduce carbon emissions to their absolute lowest, I suggest you travel by bicycle,” says Michael Farren, half in jest, of the Mercatus Center at George Mason University. (Walking would work too, if you have the schedule of an English aristocrat and the fortitude of an especially hearty Hobbit.)

But for those who want to limit their carbon footprint, without exerting themselves to the point of physical collapse, the contest boils down to one question. Bus or train?

There are many ways to slice this question. Energy expenditure per passenger, perhaps? The type of fuel being used, and its source? How many passengers are being carried — a train with one rider may be unlikely but would surely be less environmentally sound than a bus with five if they both ran on diesel fuel.
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An empty train during the early days of the pandemic. A fully loaded Amtrak train is considered highly green, even when pulled by diesel locomotives.
(Jake Blumgart)
Many transit advocates expressed disdain for this exercise. To pit the two most sustainable forms of transportation against each other in a battle royal will profit neither. But for all those transportation geeks out there, and those curious about how best to allocate scarce resources, it’s a question worth asking. Or at least fuel for the nerdiest possible parlor game.

Buses to the Front!


There are partisans in each corner of the green transit debate. In the course of Governing’s transportation reporting, advocates and experts often mention that their preferred mode is the most climate-friendly option.

In an interview last year for a story on the state of the intercity bus industry, Bruce Hamilton of the Amalgamated Transit Union (ATU) noted in passing that the gutting of Greyhound had been an environmental catastrophe.

“From the point of view of both congestion and pollution, intercity buses are the least polluting form of transportation out there,” said Hamilton, vice president of the ATU and former head of the Greyhound local. “The only thing that has less carbon footprint is walking and bicycling. You get even half a busload of people out of a car, it's just an amazing effect on carbon emissions.”

For Hamilton, buses measured up well to trains because much of Amtrak runs on diesel fuel. Outside the Northeast Corridor, which runs from Washington, D.C., to Boston, little of America’s passenger rail network is electrified. Of course, if that electricity is produced through burning coal or natural gas, then even the Northeast Corridor line would have a weaker environmental case to make. But much of this central rail thoroughfare is powered by electricity from hydro and nuclear sources.

Nonetheless, Hamilton contends that buses stack up well against their rail-bound counterparts, partly because of the costs of building infrastructure for rail service.

“When you take into account the production of railroad equipment and tracks, all of that is very carbon intensive as well,” says Hamilton. “Take the entire picture and trains are actually more polluting than the road buses, even though buses all run with dirty diesel fuel.”

For other bus boosters, utilizing the infrastructure that already exists is the crucial point. Since the 1960s, half of America’s railroads have been abandoned. A vast network of lines and stations have been erased. Re-establishing them would be both impractical and costly.

“You can definitely make a solid argument for buses over trains, in particular because of the large, fixed costs that you need to put into place for intercity passenger transportation — which we don’t currently have,” says Farren, who is a research fellow at the Mercatus Center.

American society already made a decision about how to arrange its transportation infrastructure, Farren argues. What we might like to see in an ideal world is a moot point: The infrastructure for car and bus travel has already been built out. That reduces the relative cost both materially and environmentally of choosing to go with bus over train travel. (Farren agrees that in places like the Northeast Corridor, where the infrastructure already exists, it's greener to ride the rails.)

“The argument that we need to build out a completely new kind of infrastructure to accommodate intercity passenger rail travel misses the real-world starting point,” says Farren. “In terms of the total cost in terms of green-optimized travel, you have to start from where we are right now, not from a blank slate or where you wish we were.”

But Trains Though


For the railroad defenders out there, Farren’s point is one that evokes great frustration. Taken to its extreme, it’s an argument against ever building again. After all, there’s always going to be short-term costs, emissions and otherwise, for anything. And, in any case, that kind of logic is always applied selectively, train boosters say.

“I just think that's kind of a specious argument: No one has ever used that same logic to oppose building another lane of highway,” says Jim Mathews, president and CEO of the Rail Passengers Association.

Building out passenger rail capacity would probably be a carbon-intensive process for the years of construction, but would then allow for generations of low-emission travel. Mathews points to research showing that trains emit the lowest of CO2 per passenger mile at 177 grams per passenger mile. Buses come in at 299 grams per mile, second-worst only to cars at 371 grams.
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Building out passenger rail capacity would probably be a carbon-intensive process for the years of construction, but would then allow for generations of low emission travel.
(BrandonKleinPhoto/Shutterstock)
“If we were to invest in the correct kind of infrastructure, we would dramatically reduce emissions from travel,” he says. “Would you have a short-term emissions penalty to pay? Yeah, you probably would. But that doesn't mean that it wouldn’t overwhelm the results of just sticking with buses for the next 40, 50, 60 years.”

Mathews argues that even given the diesel fueling many of America’s passenger trains, there’s an enormous advantage to the rails. A diesel locomotive pulling 300 passengers across 2,000 miles is greener than a diesel bus hauling 70 passengers even for 1,000 miles. It may not beat the bus as much as a clean electric train would, but it’s still meaningful.

That’s because modes of transportation increase in efficiency the denser they are in terms of passenger use.

“Trains are generally less problematic on a per-person perspective, because they can have more people in them per energy expended,” says Yonah Freemark, senior research associate with the Urban Institute. “A train will spend virtually the same amount of energy to move 1,000 people as it will use to move 100 people, so if you can put 1,000 people in that train it's suddenly one-tenth of the pollution.”

Is There Even an Answer to This Conundrum?


For Freemark, the buses versus train debate depends entirely on how many people are actually using the service. The more passengers that are on a vehicle, the less energy is used per passenger. Trains can carry a lot more people than buses, when optimally utilized. But how many Amtrak trains are running at full passenger capacity? A two-thirds empty diesel train probably doesn’t compare that well to a full passenger bus.

The study that Mathews cited earlier, for example, considers data from all sorts of different buses and trains across the country and calculates their overall average CO2 emissions per passenger mile. That doesn't reflect the fact that train performance can vary vastly based on the location.

“The answer to the question is not which mode is best, but which transportation line has been designed to attract the most passengers,” says Freemark. “The one that attracts the most passengers is the one that produces the least pollution.”

Considering the atrophied state of passenger rail, buses are currently the mode that attracts the most passengers with two times the ridership of Amtrak. That doesn’t mean America's passenger rail service couldn’t be reformed to attract more riders. The infrastructure act passed by Congress last year could allow for increased capacity, longer trains and more frequent service on already popular lines. Amtrak’s fare pricing could be tweaked to attract more riders of modest means, especially in areas like the Northeast Corridor where demand is high and the clean electricity fueling the ride makes it inarguably the greenest way to travel.

But even if Amtrak becomes greener away from the Northeast Corridor, buses will still be the most environmentally friendly way to travel in much of America. Train travel will not be returning to many rural areas, small cities and exurban communities, no matter how much money Congress allocates.

As things currently stand, for many of these areas even a motorcoach isn’t an option. Cutbacks to bus service in recent decades have isolated many destinations from any but the least environmental form of travel: the personal vehicle.

“That’s why there's a real need for a national bus service that connects cities, and there just isn't one anymore,” says Hamilton, of the ATU.

There is no satisfying answer to whether buses or trains are more environmentally friendly. It matters what kind of fuel they use and how convenient they are to use (and therefore more likely to tempt you from your car). Policy can focus on making buses more appealing, or even just plain available, in the places where they make the most sense. It can also be used to make train travel more accessible to more people, both in terms of cost on the Northeast Corridor or access in regions like the Midwest.

Anything to get people out of airplanes and cars.
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Cars and trucks are the single biggest contributors of carbon to the atmosphere.
(Shutterstock)
“I would think the answer is that it depends,” muses David Bragdon, executive director of TransitCenter. “I don't think there is an absolute answer to that question about modes. The point is that either of them is vastly superior to private automobiles.”
Jake Blumgart is a senior writer for Governing and covers transportation and infrastructure. He lives in Philadelphia. Follow him on Twitter at @jblumgart.