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. James says:

    Seems to miss a couple of points. First, if you have your existing electric-powered transit system running on coal-fired electricity, it is pretty easy to switch that system over to electricity generated from natural gas, nuclear, wind, or dilithium crystals. Not much you can do with petrol-powered cars if petrol becomes scarce.

    Second, I think the real benefit comes from forgetting about transit altogether. This is the 21st century: if I want something – this post, say – to be seen by perhaps thousands of people all over the world, I don’t have to hand-write a copy for each one, and send out messengers on horseback or sailing ship to carry the copies to their destinations. I just send out a few electrons & photons (fiber-optic cables) instead.

    Much work, and in particular much of the work being done by mass-transit commuters living/working in congested urban areas, could similarly be done simply by sending out those lightweight, energy-efficient electrons & photons. Why not a comparison of that to other transit systems?

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    • Rob says:

      Bingo. The key is less transit, not mass transit.

      A lot of our traffic problems would simply disappear if we could break away from the traditional office. Telecommuting is just one (although probably the best) possibility. Even in jobs where a physical presence is absolutely required, businesses could do things like extend work hours outside of the traditional 9-5 so that workers can drive or ride in outside of rush hour. Large companies might locate small satellite offices near dense population centers, rather than having a single mega-location in a central commercial district. There a tons of possibilities but little incentive for businesses to change how they work.

      I think that even conservatives (like myself) would be open to price incentives. The trick to winning them over is to make new taxes and cut old ones. It’s hard to object to a revenue neutral tax.

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      • Edgar says:

        Ah yes, telecommuting.. the newest way to get someone to work 12 hours a day for 8 hours pay. Oh, and I forgot… pay for your office equipment and supplies out of your own pocket.

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    • Travis says:

      Telecommuting is nice, but having a centralized place is also important for a lot of reasons (confidentiality for meetings, for example).

      There should be a push for people to stay home more often and work from home though. Along with a push to get people to live closer to their workplace. Doing these two things would reduce CO2 Emissions far far more than any amount of mass transit ever could.

      I do think we’re beginning to see the start of such movements though. Here in CA traffic is very reduced every Friday. I suspect its because people tend to telecommute on friday.

      Now that you make me think about it, I think a Freakonomics episode on telecommuting would be amazing. It could address the failing of the “hour / wage” model in many forms of work, in favor of a “contract completion” model, as well as things like reduced overhead from requiring less office space, and finally other positive externalities like reduced congestion and CO2 emissions.

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      • James says:

        Confidentiality for meetings? First, it’s trivially easy to encrypt any data stream going over the internet. Second, just think how much the productivity of the typical worker would increase if we didn’t have to waste time in meetings.

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    • Joe j says:

      ” it is pretty easy to switch that system over to electricity generated from natural gas, nuclear, wind, or dilithium crystals”
      LOL good joke, because it is actually near impossible to switch.
      Nuclear, the last new one ground broke in 77. unless you consider 45 years to be quick or easy..
      Wind? only is semi useful in certain locations and with electrical transmission losses what they are, is mostly a joke.
      Nat gas is a possibility, but again another fossil fuel.
      Dilithium crystals. lol

      Cutting down transit, is possible. Just run into the problem of convincing 100s of millions of people with different wants and desires and lifestyles to forgo all that.

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  2. Tim Johnson says:

    This might be bad for liberals and conservatives, but good for libertarians. Decrease public spending on unnecessary items while raising consumption taxes? Sign me up.

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    • Travis says:

      I thought Libertarians were opposed to consumption taxes… Pigovian tax would be ideal in this situation, though.

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  3. Speed says:

    In order for any mode of transit to gain ridership it must provide service from where people are to where they want to go. In the decades since the hayday of municipal rail and bus, people have moved from concentrated multi unit apartments to single family houses in the suburbs and beyond. Similarly, jobs have moved from large factories and office buildings with thousands of employees “downtown” to smaller facilities in office and commercial parks — once again in the suburbs and beyond.

    It is unlikely that central planners in the US can reverse this trend in any time frame shorter than decades. And if they do, what happens to all the abandoned real estate?

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    • gevin shaw says:

      Of course, it was “central planning” that built the freeways that made the suburbs possible. And it took decades. Not disagreeing with you, just noting that there’s always a balance between meeting a demand, and creating it.

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      • Speed says:

        The interstate highway system was designed and built to carry traffic between cities — which may be why it is called the INTERSTATE highway system. An unintended consequence is that it allowed people to move farther from the city center and commute by car. The central planners, always being the last to know, followed up by building networks of freeways in and around cities to serve the locals.

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  4. Sean says:

    I live in Calgary, Alberta (Canada) and our public transit system consists of both light rail and buses. During morning and afternoon rush hours, the entire system is oversubscribed. Stories are common about people waiting on a cold morning for a bus and unable to get onto it when it arrives because the bus is already full to bursting, and so the commuters must wait for another one. The trains are jam packed.

    The point is this: during the middle of the day once everyone is already AT work or school, yes of course buses and trains run at lowr occupancy. This is to be expected. For the very same reason there are fewer cars on the streets at 2 PM then at 8 AM. This should be factored into calculations… How much less energy per capita is a jam packed train using than all those vehicles stuck idling in a traffic jam during commuter peak times?

    Secondly, notwithstanding the above, I actually think that the majority of the users of the system have their own incentives to use mass transit that have nothing to do with CO2 emissions. Some of those reasons include the very high expense of parking in our city (which is amongst the highest in North America), lack of available parking at colleges and universities, the desire to avoid heavy traffic, people who don’t own cars, and so on.

    Now, the net result of so many people using mass transit during rush hour is that there are indeed fewer cars driving around, which means less pollution, but I would strongly argue that’s really just a handy side-effect, a positive externality, to providing people with the means to move around without driving themselves.

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  5. Colin says:

    Interesting points and a worthwhile read.

    Not directly related to the environment, but what about productivity losses due to commuting or driving? Where I live, and I imagine this is true in many other areas, mass transit doesn’t save me time. For some, I’m sure mass transit avoids being stuck in traffic and actually saves time and not just hassle, gas, CO2, etc.

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  6. Joel Upchurch says:

    Brad Templeton has been engaged in these issue for years. Read this on his blog.
    He does a lot of analysis on robocars and robotaxis. I’m interested in robobuses, where people can connect into a website where say their stop and the destination and time. The system then texts you your pickup time. The buses won’t run when there is little demand. The current system where people drive the buses and the drivers keep driving even when there is no demand is very inefficient.

    The problem with current cars is that the cars weight too much and they haul too much dead weight around. If the average vehicle weighed a few hundred pounds, then the BTU per passenger mile would skyrocket.

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    • BikerDad says:

      “The problem with current cars is that the cars weight too much and they haul too much dead weight around. If the average vehicle weighed a few hundred pounds, then the BTU per passenger mile would skyrocket.”

      That’s a problem that’s also a benefit. That “dead weight” helps keep the occupants from being dead. Yes, you can design a “car” that only weighs a couple hundred pounds. It also will only carry one person, it takes so long to get up to speed that granny drivers run it over, and when it gets hit, the occupant has barely more protection than a bicycle. Oh, and it has no a/c and no heat, and gets blown all over the place.

      Now, if we completely rejiggered our entire transportation system, all of these shortcomings could probably be addressed. Catch is, we don’t get to just swap out our existing system with the “optimal” system overnight.

      The most “efficient” motorized transportation is the moped. Why not just use those?

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      • Joel Upchurch says:

        By your logic motorcycles would be outlawed and everyone would be required to drive an SUV. We could build a vehicle far safer than any motorcycle at a fraction of the weight of a common passenger vehicle. The real way to reduce passenger deaths on the highway is to get rid of manually driven vehicles, since it isn’t the vehicles that are dangerous, but the drivers.

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  7. John Halunen says:

    Pretty sure bicycles blow the doors off the efficiency of mass transit even in NYC? Would help with our obesity problem too.

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    • Rob says:

      Great on paper but it falls apart in reality. Are you going to pick up the kids from daycare on your bike? What about grabbing drive-thru on the way home? No stopping by for eggs on the way home either. Am I riding to work in my business casual clothes or trying to change in the men’s room before and after? How long is too long for that bike commute anyway? My 20 minute drive turns into an hour long bike ride. I could use the exercise but I can’t afford to spend the time.

      The realities of the urban landscape pretty much make bike commuting a fringe behavior, however admirable it may be. Good for you if you can pull it off but it’s simply not an option for most people.

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      • James says:

        All those “problems” have ready solutions. If you’re one of the small fraction of the population who has kids in daycare (I’m not), you can haul them in a kid trailer. There’s no reason you can’t ride your bike through the drive-through, or – I know this may come as a shock to some – you can actually PARK IT and go inside to place your order. Likewise, I’ve frequently carried a couple of bags worth of groceries in my bike saddlebags.

        As for the time factor, say that the commute by car takes 20 minutes, and you need an hour of cardiovascular exercise per day for health. That’s 80 minutes total, but if you commute by bike, you combine them and save 20 minutes.

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      • Sandy says:

        I commute by bicycle about 12 miles (round trip) five days a week. I know I could adjust to a longer commute, but I have to admit this is about as long as I’ve ever had to ride on a daily basis. I can’t honestly tell you how much farther than that would be too far. I used to haul my kids to and from school in a bicycle trailer, but they are much too old for that now. They ride the bus to college by themselves. I stop at the grocery store quite regularly, and yes, I even manage to bring home uncracked eggs. I usually change clothes at work, but sometimes bike in the clothes I’ll wear when there. You’ve got me with the drive-thru, though. I get off of work at midnight, when the dining rooms of those places are usually closed, and I’m not always successful in getting served while on a bicycle. My point is that none of your objections are really significant to somebody who wants to commute by bike. If you’re too lazy to do it, that’s fine. I’m a pretty lazy person myself. I wouldn’t have gone to the trouble of figuring out which drive-thrus I can be served at on my bike in the middle of the night if I wasn’t such a fat, lazy slob. I can admit that my weakness for cheeseburgers is my own problem. You should admit that your belief that biking to work is impossible for you is not due to the “realities of the urban landscape” but rather to the reality that you are too lazy to do it. Don’t try and run me off the road, and please don’t try and talk others out of it, as more cyclists on the road does more for my safety than the helmet I almost always wear. If you can not do those two things, I think we can each pursue our own lazy lifestyles in peace.

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  8. Derek says:

    It seems like best solution is to start building cities to look more like New York, dense urban centers are more efficient in almost every way and are generally the biggest wealth producers in the world.

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    • Molly says:

      “Best” for mass transit, not for raising families, living in a low-crime area, or having my preferred quality of life. No way in this world would I want to live in NYC.

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