Can Mass Transit Save the Environment? Right Wing or Left Wing, Here’s a Post Everybody Can Hate

(Photo: RJ Schmidt)

A major rationale — perhaps the major rationale — touted by supporters of mass transit is that by reducing our output of greenhouse gases and other pollutants, transit can help save the environment. The proposition seems intuitive and even obvious: by no longer encasing each traveler in thousands of pounds of difficult-to-move metal, surely transit is more energy-efficient. Plenty of analyses prove this. But then again, Aristotle, who was revered as the infallible font of truth for more than 1,000 years, proved that heavier objects fall faster than lighter ones and that women have fewer teeth than men. Might studies that demonstrate transit is greener be similarly wrong?

They might. The reason is that many studies of energy efficiency by mode often make questionable and — depending on the author’s point of view — self-serving assumptions. The main trick is to look at autos with but one passenger and compare them to transit vehicles in which every seat is full. (For example, see this.)

But in the real world, this is emphatically not the case. At any given time, the average auto has somewhere around 1.6 passengers, and the average (typically 40-seat) bus has only about 10. Rail vehicles typically have more passengers (on average about 25), but then again they are also typically much larger. Thus their average load factor (percentage of seats filled) is also not high, at about 46 percent for heavy rail systems (think subways in major cities) and about 24 percent for light rail (think systems that mostly run at street level).

It is not clear that moving around large and largely empty vehicles is much of an improvement over moving around smaller ones. In fact, it may be worse. According to the Department of Energy’s Transportation Energy Data Book, in 2010 transporting each passenger one mile by car required 3447 BTUs of energy. Transporting each passenger a mile by bus required 4118 BTUs, surprisingly making bus transit less green by this metric. Rail transit admittedly fares better, at 2520 BTUs per passenger mile, but even this is not the kind of slam-dunk advantage over the auto that transit advocates might hope for. 

There are some qualifications here, some of which aid transit and some the car. The sources of transit’s energy—electricity in the case of rail, and often natural gas in the case of bus—are typically cleaner than those of the auto, so that even with higher energy usage, transit may produce fewer greenhouse gases. Still, even taking this into account, a bus produces more CO2 per passenger mile than the car for most trips.

Transit looks better when the environmental costs of building the vehicles and infrastructure are spread over the passenger miles that each mode will accommodate. Taking this into account, an average bus at normal load factors does currently produce slightly fewer pounds of CO2 than autos, and rail transit does much better.

On the other hand, electricity is not much cleaner than gasoline if it is derived primarily from coal, and in some states, such as—surprise—West Virginia, nearly all of it is. And in any event, the electrification of autos is advancing. Moreover, greatly increased fuel economy, even for regular old internal combustion vehicles, is rapidly making cars more efficient. By the time the new fuel economy standards for autos are reached in 2025, a new car’s average mpg will have increased from 27 to about 40, meaning that in terms of energy efficiency, cars may leave buses behind and begin to be competitive with rail. 

Does this mean that efforts to increase ridership will not help—and may even harm—the environment? Not so fast. In fact, the environmental benefits of higher transit ridership might be very great—but they depend completely on how those increases are obtained.

Pumping up ridership by adding transit service will probably do little good, and may even be counterproductive. The reason is that new service promises to reduce transit’s already less-than-spectacular load factors and result in largely empty vehicles.

Why? At this point we have picked all the low-hanging fruit in terms of transit markets. We already have extensive rail transit service in the places where land use and demographic characteristics are congruent with high transit use—such as central Chicago, Boston, the San Francisco Bay Area, Washington D.C., Philadelphia, Los Angeles, and (writ very large) New York City. For the most part, any new transit service has to go to relatively low-density cities and low-density areas within cities, meaning that new investment would drag transit’s overall efficiency down, not up. 

To give an idea of how this phenomenon works, the heavily used New York subway system (58 percent of seats are typically filled) produces .171 pounds of CO2 per passenger mile, less than 1/3 the average for cars nationwide. However, the much more lightly used Cleveland, Pittsburgh, and Memphis light rail systems actually produce considerably more CO2 per passenger mile than cars do. Unfortunately, due to diminishing returns, new rail transit systems are more likely to resemble the latter three than the former one.

On the other hand, if we can persuade travelers to leave their cars and ride existing transit service, rather than new service, the environment will benefit greatly. Given its current low load factors, transit generally has plenty of capacity to absorb new customers with practically zero additional energy expenditure.

Strategies to pursue this would involve economic incentives to influence behavior. These might include pull strategies designed to lure riders onto transit, such as fare cuts, or push strategies designed to get them out of cars onto transit, such as increasing gas taxes, congestion tolling, or charging market rates for street parking. Note that pricing strategies of this sort would also help the environment by raising auto efficiency through increased incentives for carpooling. 

Thus it makes more sense to focus on policies that attempt to change travel behavior as opposed to building infrastructure and buying vehicles. However, public policy in recent decades has self-defeatingly focused on the latter strategy, not the former. This has proven very popular, since shiny new trains and buses allow politicians to take credit for very visible improvements, while the costs of said infrastructure and equipment are essentially invisible since they are spread broadly across the American public and are hidden in arcane budgeting processes. (With a thicket of passenger fares, fuel taxes, sales taxes, bonding, advertising revenue, etc. coming from federal, state, regional, county, transit district, and municipal administrations, it can be difficult even for experts to determine who pays what for transportation.)

So there it is: to benefit the environment, probably the best thing to do is be very skeptical about adding new transit service and even to discontinue some service we are currently providing (sorry, liberals). Simultaneously, we should raise fees and taxes for driving (apologies to you conservatives). The best I can offer to keep the comments section below free of hate posts is that at the moment the chance of either happening is small. This may make good sense given the current political atmosphere—but it makes little sense for the atmosphere of the planet.

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  1. none says:

    The big problem with mass transit is that the greed of a very few can shut down a city. Consider the transit strikes when the very well paid union ‘workers” were too lazy to come to work for several days. Enough to cripple everything.

    If everyone has a private car, and a few people decide to be antisocial and hold the entire city hostage to their greed and refuse to drive, nothing happens. Life goes on for everyone as usual.

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  2. Daniel N. says:

    Way to take jet plans vs. trains into account. That’s where all the CO2 reduction comes from. Are trains mass transit? I don’t know, but we need more electric trains that run on wind and solar electricity and less planes that run on fossil jet fuels.

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  3. Jack Marson says:

    On the relationship between coverage and environmental efficiency: The low ridership lines help feed the efficient, high ridership lines, thereby making them more efficient. For roads, we recognize an elaborate hierarchy feeding each other, and don’t say, “If it’s under 10,000 ADT, it’s toast!”

    Having a strong network of transit lines in time and space makes people more willing to reduce their car ownership. That of course leads to more transit trips and fewer car trips.

    I would also think that being able to create locations served by multiple transit lines would be more encouraging of more transit use, less car use, and more transit-oriented development.

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  4. john says:

    The author misses the point. Car ownership is a catalyst for urban sprawl. Urban sprawl, scientifically doesn’t make sense, it’s an unsustainable system of development. Yeah mass transit has its problems but it would work better if people lived nearer to where they work and play. The suburban model is an empty promise. It takes too many resources per person to keep it up. I think the vast majority urban planning community under the age of 40 feels this way. You can attack something on how it works but why stop there? The system could work under a different system. In a way your right. Adding light rail might not be the best idea with regards to the environment as of right now, but it is a step in the right direction. The suburban standard is unsustainable and by definition will come to an end at least for the middle class. Sprawl is unhealthy on a social, economic, and environmental level. We can’t have our cake and eat it too… forever anyway.

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  5. Mark J. Ambrose says:

    There is just one problem (and it is a fundamental one) with the argument presented in this post. When one evaluates the costs and benefits of any decision, one doesn’t care about the resulting averages, one cares about the margins.

    So, if one considers expanding the bus system in a certain city, the comparison should not be the avg. C footprint of all bus riders in the city vs. the avg. C footprint of all who drive. It should be the avg. C footprint of all the new bus riders who switch to using transit because of the expanded system vs. the C footprint that they had driving their cars before switching to transit.

    Now this is a harder number to get at than the overall averages. To get it we have to know something about who is likely to switch to using transit. However, my guess is that the typical person who might switch to transit is more likely to have been commuting in a single occupant vehicle (simply because family units who combine trips probably will still do so and carpoolers as well). Similarly, we have to estimate the marginal C cost/passenger of the expanded system (somewhat easier to do using fuel and ridership numbers for the original and expanded system).

    Looking at things this way, all the low-hanging fruit may not be gone. There may still be a number of areas where expanding transit systems makes sense in terms of carbon footprints.

    The same sort of analysis, looking at the margins, needs to be applied to any reduction in transit service.

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  6. David says:

    Just the sameas in the book you get basic science wrong, so why would I trust your economic analysis?
    Heavier objects do not fall faster than lighter objects, except in extreme cases such as a steel ball vs a ping pong ball or other situation such as sheet of paper vs a ball of paper where wind resitance effects change the outcome.

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  7. L Leeman says:

    I wonder..would all the ‘transit.. it will save the PLAnet!’ zealots stay in harness IF the problem could be reframed and solved a different way.

    I mean if you could operate cars (and I just mean fueling them, not building or maintaining them) with NO emissions that could be construed as harmful, and you could do the same for subways and buses, would you still choose to ‘get them out of their cars’ and in the case of a city poorly served by transit, still try to ‘get them out of their cars’?

    On the one hand, you have a system (cars) that is mostly direct to destination, no matter where the destination is. It also serves destinations where buses and trains do not. It is not time sensitive, meaning, you can use it any time of the day or night and usually get close to the same result. It is comfortable and personalized. lhe roads it uses are, in large part, necessary in any case, to transport food, clothing, medical assistance, building materials, policing, etc. etc.

    On the other hand, you have trains and buses(really big, heavy cars) that, depending on the trip taken, will usually NOT go direct to destination, and definitely will not go direct to many(even most) destinations because there is no service. It is time sensitive, and will likely give you less or no service if you work at night. It is not personalized, in peak hours it is uncomfortable, and mostly, you can’t ship things on it. The roads the buses use are, in large part, necessary in any case, for the same reasons as the car case. You may build fewer roads, but balancing that, you build very expensive dedicated track or blacktop.

    Critically, PEOPLE ARE NOT WILLING TO PAY FOR IT VOLUNTARILY when given the choice to pay for a car system instead. This could probably be argued, but my money is on it being emphatically true.

    In a city like mine, where transit is being touted mightily and there are very few trains and not yet any subways, the massive cost of building such a transit system is yet to be committed. If, instead, we could alter the fuel that drives cars, would we then choose to spend the billions on building a transit system?

    Rather, what if we, and all the other cities reaching a certain size, that could concievably practically operate a sucessful transit system, pooled our uncommitted billions to transition to hydrogen or electric vehicles. Would we then be at all intereted in Big Transit?

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    • Nathan says:

      Car use in this country is HEAVILY subsidized by the federal government. If car drivers were forced to cover the costs of their driving habits directly (as opposed to it being paid out of income tax revenues and other sources) people would drive far less than they currently do. And that’s not considering the cost of the environmental damage that widespread car usage has caused. People are willing to pay for cars over buses because the price of cars is artificially cheap.

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  8. Nathan says:

    Because environmental factors are the only reason we have public transit, amirite? There’s no need to consider the cost of parking and road construction vs transit infrastructure, the ROI on that infrastructure, the damage that sprawl causes (which is enabled by increased car usage), the fact that having effective transit options actually changes land use patterns, the fact that more densely populated areas simply can’t support the number of cars that suburbia can on strictly a space basis. None of that is a good reason to promote public transit over cars, right guys? Of course not.

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