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.


Hm, one thing I'm wondering is, by taking a car off the road when converting a driver to a commuter, does that reduce congestion in the roads, thus leading to an increase in gas mileage for drivers? If that's a large enough effect, should the lowering of car pollution due to the higher MPG be credited to public transit, not to cars?


Reducing congestion also incentives more people to drive

Michael Peters

But no more than before. Capacity hasn't changed you've just reduced congestion so it's still a net win for everyone.

Laurent Duval

Are averages really pertinent when discussing mass transit load ratios ? I mean, if you're taking a subway ride at rush hour on a very busy line to commute between your home and your workplace, you won't suddenly switch to that very quiet line over there, far from both, just because there's an incentive to use mass transit more. Of course, adding more overloaded buses, subway cars and trams on busy lines will raise the average, but at the probable cost of more users opting out due to discomfort (or even insecurity, as it's the case in my city, Paris).

nike air max 95 sale nike mercurial football
nike air max 95 sale

[WORDPRESS HASHCASH] The poster sent us '0 which is not a hashcash value.


Here in Wales ,one gets a free bus pass at 60 years old- this is the best incentive for me to use the bus and according to your article I'm only filling an otherwise empty seat- my partner and I only need one car between us ,the car gets used less so lasts longer and congestion and CO2 are reduced. I must be in eco-heaven already -and if you get on the double decker the view from upstairs of the hills one side and the sea the other is stunning.

football boots nike mercurial nike roshe run mens red
football boots nike mercurial

[WORDPRESS HASHCASH] The poster sent us '0 which is not a hashcash value.


The answer is autonomous cars. Distributed, flexible, & minimal infrastructure costs.

nike air 90 max nike air max size 7
nike air 90 max

[WORDPRESS HASHCASH] The poster sent us '0 which is not a hashcash value.


You might also consider that having a car also encourages people to travel longer distances than they typically would just riding mass transit. So even if the passenger mile efficiency is worse it could still lower emissions overall due to fewer miles traveled.


How does having a car incentivize people to drive longer distances? I would think the opposite could be true. If you are driving somewhere, you can take the most direct route. When you have to use public transit, you might need to make a few transfers or take a line that is not as direct.


I don't think "longer distances" in this case means taking a longer route to the same destination, it just means driving more often. Personally, when I am taking the bus, I organize my errands more efficiently, whereas when I have a car and can drive from one side of town to the next twice a day on my own time if I want to, there's less incentive to limit my trips. (Obviously I will have to still have to pay more for gas, but that is a delayed negative consequence and doesn't affect my decisions as strongly.)


I see a lot of sides to this debate and one is on the price component, specifically those that argue it's too expensive of a project to take on...but do the detractors pay attention to the cost of car ownership?

Wow...$8,946 for the average sedan and $11,370 for the average SUV...ANNUALLY. Now multiply that out for the number of vehicles on the road (there are stats for that, too)...

So let's take the lesser figure ($8,946) and reduce the total number of cars by just 1% (2.5 million cars)...and redirect those funds. Hey, we just came up with $22.3 billion.

Yes, it's much more complicated than that...just pointing out the argument of "I don't want to pay billions for my transportation" is seriously jaded as we already pay trillions annually to this for our cars. If we could convert auto manufacturing plants quickly to create tanks for the military in the 1940's, surely we could convert empty factories (or live ones, for that matter) to create parts necessary for rail in the 2010's, right?


joe J

The real problems with your math is. Althought 1% sounds small it is actually huge to get that many people to change their life style. Even if they took mass transit they would still have cars to go places mass doesn't go. so reduce it to .01% change. And compare that to the cost of just Californias light rail that some are pushing which is projected to be $100 to 300 billion, for just that project alone. So even if this project stopped every single Californian (about 2% of the country) from having a car. it wouldn't be close to cost effective


You're comparing the gains from reduced car ownership, which are annual, to the total cost of California light-rail. So, in your example, we'd break even within 5-15 years.


I'm surprised that in your final paragraphs you didn't talk about the central factor that makes mass transit work - population density! If you can't build high density housing near your mass transit stations, then yes it is pointless, but if you can then it clearly seems worth it.


This is clearly the point missing from the article. The suggestions in this article are all focused on HOW people get places, not WHERE they are going from and to. The biggest problem the US has in terms of transportation is the truly insane development patterns post-WWII, which got really bad by the 1980s and 90s. Only in the last 10-15 years have we started to rethink our concepts of development and start to... not exactly move toward a more sustainable kind of development, but at least move away from the truly absurd, 100% car-oriented modes of development we have used for the last 50 years.


The "problem" is that in the U.S., people are free to live where they like and go where they like, stay as long as they like, and shape their own plans. The "problem" is freedom.

I live in Ohio, where there has been talk of building a supposedly high-speed rail link from Cincinnati to Columbus and Cleveland. It would cost a fortune to build, and not be high-speed until another chunk of money is spent. It sounds so good--until you think about this question: why would people who can drive--and have the options I mentioned above--choose the rail instead? If you take the rail, you have to leave the business trip--or the family event or baseball game--according to the rail timetable. If you're shopping, you won't have the trunk and back seat of your car to carry your loot. And so it goes.

So, yes, the fact that people get to go where they want--as Steve and many planners lament--is the "problem" that makes many mass-transit plans untenable.


Enter your name...

I didn't think that greenhouse gas emissions were really a big goal for promoting mass transit. After all, we started promoting mass transit even before anybody knew what a greenhouse gas was. I thought the main goal was to get more people to/from work during rush hour (in particular) without having to waste real estate and infrastructure on places to drive and to park quite so many cars.


In the US, especially here in CA, the CO2 argument has been used a lot recently. Basically, whatever argument the proponents think is currently the trendiest is used. It has been about the environment, creating jobs, helping traffic, and myriad other half-truths.


Triclops, your comment implies that there's some sort of evil agenda that proponents of public transportation have, which they mask with "trendy" arguments they don't really believe about jobs, environments, traffic, or CO2. So what is that hidden agenda? The only people who really have hidden motives here are the contractors who build the rails and busses, which I believe would account for a small percentage of the vocal supporters of public transportation.

For the rest of us, it's because we actually believe the arguments in support of public transportation. These arguments might be half-truths or flat-out wrong. People can believe things that are false. But that doesn't mean we're just bandying trendy arguments and half-truths to mask our real motives.


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?



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.


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.

Tim Johnson

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.


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


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?

gevin shaw

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.


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.


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.



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.

Joel Upchurch

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.


"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?


Joel Upchurch

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.

John Halunen

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


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.


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.


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.


"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.


"we have picked all the low-hanging fruit in terms of transit markets... 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"

In the medium to long-term, this is not really true. Transit enables density and walkability. Building transit to a new area will create a new transit market, as long as zoning allows/encourages. The Orange Line (Rosslyn-Ballston corridor) in Arlington, VA is a great example.

Philo Pharynx

Examine the density of Orange County, California. I live there and it would be difficult to imagine a system of transit that would work efficiently without completely redesigning the entire county. This is the sixth most populous county in the US, but geographically the cities are packed in with no space between most cities. For transit purposes it acts like a single large city with the density of a suburb and no center or downtown. Any solution would be a web of lightly-used lines.

Deron Lovaas

I am an advocate for public transportation, and I agree with much of this analysis. Transit investments need to be carefully targeted so we don't end up with stranded assets, which we can't afford especially now. And the factor that matters most is load factor. If that can be driven up through cost-effective tools like pricing and land use policy changes then the investment can pay off. Would be useful to see an analysis of transit lines nationwide based on load factors, both a snapshot of current conditions and projnections. Would show which are thriving, which are struggling or failing, and which are in the middle.


Overlooked is the key consideration of transportation:

We don't transports ourselves from place to place for the benefit of the environment. We do it to get from place to place. While it may be worthwhile to consider the cost to the environment (whether increased CO2 qualifies as a "cost" is a separate question), if we don't consider the cost to people (taking 2 hours to get to work rather than 30 minutes - which depending on where you are can give the advantage to the car or to the transit), then the economics truly is freaky, and not in a good way.

"So let’s take the lesser figure ($8,946) and reduce the total number of cars by just 1% (2.5 million cars)…and redirect those funds. Hey, we just came up with $22.3 billion."

Redirect it how? The individual shelling out those $8,946 has the CHOICE of doing so, and benefits directly. If they want to redirect it, by, say, dropping $3,000 on a good scooter and then paying $100 a month for the next 5 years to run it, thus saving $30,000, that's their choice. Mass Transit in this country is NOT choice driven. Can a market in mass transit even exist? Perhaps. We can certainly get closer to one by de-regulating and opening up the coach/taxi markets.

That, btw, would be an interesting thing for Freakonomics to examine. Open vs closed taxi markets.

fwiw, I happen to love trains. They just aren't economically practical for transporting people in most of America.


Ian M

"On the other hand, if we can persuade travellers to leave their cars and ride existing transit service"

Two big problems
1) The transit system is stuffed to overflowing at times when people most want to use it
2) The incentives are small when the transit load is light. Yes the bus has empty seats in off-peak times but the buses are further apart time wise while the car traffic is light and parking is cheaper.