Does Public Transportation Save Energy?

Our second contributed article from Bob Fischer.

Bob Fischer is a climate scientist in New York City, specializing in ice sheet / climate interactions. He has a longstanding interest in Earth Science and in advanced technology for worldwide sustainable development. Before becoming a climate scientist, Bob was a Wall Street Quant for a decade. Bob lives in New Jersey. He is a proud owner of an electric bicycle and a daily user of the George Washington Bridge.

The article is the maiden voyage of Bob’s new blog Jersey Biker, which will focus on transportation issues in New Jersey.

Ever since the gas crises 1970’s it’s become environmental dogma that getting people to park their automobile and hop on a bus or a train will save energy.  In the 1970’s, when American automobiles achieved 15mpg if they’re lucky, that was certainly the case.  But a lot has changed since the 1970’s.  How should the environmentally conscious traveler and urban planner think about transportation and energy use today?

The answer is complicated, but also surprising.  Let’s consider local travel (commuting) and long distance travel separately.  Most of our transportation energy is consumed in local travel, so that is what we will consider in this article.  Long distance will have to wait.

Local Travel

Let’s look at the typical energy use of some public transit systems, and then compare them to our favorite automobile in the driveway.  Let’s look at the DOE Transportation Energy Data Book Chapter 2. Not surprisingly, public transit systems vary in their energy use: light rail systems use between 2,000 (San Diego, CA) and 30,000 (Kenosha, WI) BTU per passenger-mile.  Similarly, heavy rail systems vary from 1,800 (New York City) to over 10,000 (Cleveland, OH) BTU per passenger-mile.

How do we evaluate whether or not these systems save energy?  It depends on your perspective.  Let’s suppose you’re environmentally conscious and you drive a Prius.  Your rated 51mpg in the city translates to just 2,254 BTU per mile.  So even if you drive alone, you will be more fuel-efficient than all heavy rail (subway) systems except those in New York City, Atlanta GA and Oakland CA — which are apparently only marginally more efficient than a single-driver Prius.  You will be more fuel-efficient than all light-rail systems except those in Stockon CA, Los Angeles CA, San Carlos CA, and Alexandria VA.  And you will be more fuel-efficient than all commuter-rail systems in America.

Now consider that US fuel economy standards are set to steadily rise, to 54.5 mpg (2110 BTU/passenger-mile) by the year 2025.  That means that by 2025, today’s Prius will be below average in fuel economy, and everyone can expect to drive a car that’s more fuel-efficient than all but a few transit systems.

Hmm… transit systems don’t save energy?  How has it come to this, after we were told for decades that we should ride the bus to save energy?  Basically, busses and trains were always designed with fuel efficiency in mind, whereas that was not on the agenda for automobiles until recently.  Automobiles have been improving steadily, whereas there is not so much room for improvement on transit vehicles — especially not electric ones.  Moreover, transit vehicles suffer from many inherent inefficiencies due to the nature of shared service: extra weight per passenger to make vehicles large enough to walk around in, frequent stops, and low seat utilization.

The last one is worth considering: a hypothetical morning rush-hour bus/train that starts in the suburbs picks people up along the way, and dumps a full load downtown will only have a 25% seat utilization.  That’s 50% on the way in and 0% on the way back out.  So even if it’s standing-room-only by the time you get off downtown, the average seat utilization of the system as a whole can still be relatively low.  On the other hand, automobiles have only a 25% seat utilization if you don’t car-pool, which is not so different from what one could expect from a transit system.

So busses and trains aren’t so much better as we were led to believe.  What should we do about this in our decision-making?  It depends on who you are and what decision you are making.

  1. If you’re trying to get to work in the morning rush hour in a city with a crowded transit system, you will save the most energy by car-pooling.  Even if you only have a 30mpg Corolla, two of you in the car will still save energy over any transit system.  And by driving, you relieve the transit system of having to run more busses or trains.
  2. If you can’t car-pool, just buy a Prius.  You’ll still do better than almost any transit system.
  3. If you do a reverse commute, the things look very different: now you will save energy by taking transit — and lots of it.  You are taking advantage of “free” seats that won’t be filled anyway, making your effective energy use zero.

Carbon Footprint

Since I’m a climate scientist, I don’t really care how much energy you use, as long as you didn’t generate CO2 in the process.  What I DO care about is your carbon footprint.  So let’s look at the comparative carbon footprint of these different modes.
From the carbon footprint point of view, automobiles aren’t looking so hot anymore, nor are busses.  Why?  Because the only way we know how to power them is with carbon-intensive petroleum.  The New York City Subway, which runs on electricity, 30% of it nuclear-generated, now looks like a clear carbon winner over anything you can drive.
Unless you drive an electric car, of course.  And aren’t electric cars great: new cars such as the Chevy Volt and Nissan Leaf get anywhere between 100mpg and 200mpg equivalent, depending on who you ask and how your electricity is being generated.  Now, the efficiency winner tips back away from the transit systems.  Electric cars have the same carbon advantages over petroleum as do electric trains.  If nothing else, switching to an electric fleet will allow us to move away from petroleum for transportation, toward other cheaper primary fuels: for example, coal, solar, nuclear, wind, natural gas, hydro — pretty much anything in the days of $100/barrel oil.

Smart Growth and Transportation Planners

What does this all this mean for city planners?  Rather than trying to build busses to the exurbs, it seems the best way to save energy on transportation is to decrease demand for it.  And we know how to do that: build denser, more compact cities where the places people live and the places they shop and work are closer together.  The term “Smart Growth” embodies this philosophy.

And it works.  Whereas transit usage is uniformly low almost everywhere, Total Vehicle Miles travelled per day varies greatly among American cities.  Not surprisingly, New Yorkers travel less than anyone else on average (9 miles/day): travel by any means is slow and difficult, and there is so much so close anyway.  And suburban New Yorkers, who drive through densely-packed suburbs, drive less than almost anyone else (17 miles/day).  Even Los Angelenos, famous for their car culture, don’t drive that much: 23 miles/day.  In contrast, Houstonians drive an average of 38 miles/day.  Think about it: driving a Prius in Houston will have a greater carbon footprint than a Corolla in LA.  And if you live in New York City, you might as well drive a mini-van or SUV.

So where does transit come in?  The problem is, compact cities quickly become congested, and there’s no place to park all those Priuses anyway.  Transit enables cities to grow at higher densities than would otherwise be possible using just automobiles.  Transit does not save energy directly.  But it is a key tool we have that allows us to save energy by building compact cities.  Even in “transit-oriented developments” being built today, the overwhelming majority of people drive.  But they drive less, and that is the key.

What does this mean for the transportation planner?  In building new cities, we should plan for transit via bus lanes, rights-of-way, etc.  But there’s no need to actually build and operate the transit lines until congestion creates demand.  That is 180 degrees different from the more common approach today, in which we do anything we can to entice people out of their cars.  The problem is, once we’ve built a non-compact city, it doesn’t matter what form of transportation we use to get around it, we will be stuck with high energy use.

There are other good reasons to build transit systems as well: they require lower capital costs for the vehicles, use less infrastructure per capita, use less land in the city centers, and provide universal mobility.  But they only really work well in relatively dense, compact areas.

The Ultimate Carbon-Friendly Transportation

If riding the bus doesn’t win eco-points over driving your Prius, what’s the serious eco-warrior to do to get to work?  The answer is the bicycle.  But not just any kind of bike.  Read on…
It’s well-known that bicycles require less energy to move forward than any other vehicle known to mankind.  They are so efficient because they are extremely light-weight, they have low rolling resistance, and they don’t go fast enough for that efficiency to be killed by their bad aerodynamics (25 mph and up).  So bikes are really efficient to push around, and twice as efficient as walking.
The big problem with bikes is their inefficient power plant: you.  Because you eat food grown through our commercial agriculture system, which is incredibly inefficient.  For example, 40 calories of fossil fuel energy are expended for every calorie of beef protein produced at your table, ready for you to eat.  Other foods seem to be better: grains require only maybe 10 calories of oil per calorie of food.

So when we take our agriculture system into account and look at biking vs. our trusty Prius, how do things  stack up in the end?  If you’re a couch potato and need the exercise anyway, then the bike is a clear winner.

But suppose you’re already fit, now you’ll have to eat more when you bike.  If you eat bananas to power your bike, you’ll apparently come in at 65g CO2 per mile.  That compares with 220g CO2 per mile for a Prius.  Definitely a lot more efficient.  But if you and your three buddies want to get somewhere, you’ll do less harm to the planet driving your Prius.  And if you’re a carnivore and love your cheeseburgers… well, you might as well just drive, the cheeseburger-powered bicycle apparently does 260g CO2 per mile.

If biking doesn’t save much energy after all, what’s the eco-conscious bike lover to do?  The answer is this new invention that came out of China over the last decade: the electric bike.  At first, it seems like “cheating:” surely a motorized vehicle will have a higher carbon footprint than a manual bicycle.  But our electric grid is (thankfully) far more efficient than our agriculture, giving electric bikes a significantly lower carbon footprint in the end.

All-in-all, my electric bike uses about 10% the power of a Nissan Leaf — which translates into somewhere between 1,000 and 2,000 mpg electric equivalent.  The vehicle has a top speed of 20mph, goes for 30 miles on a charge, and requires so little power to recharge it’s not worth metering: someone once e-biked across Canada using only $10 of electricity.

So there it is.  The electric bicycle is the most energy-efficient, lowest carbon-footprint way to get around that’s known to mankind.  Eco-warriors, take note.  Even if you charge up your bike on the dirtiest coal-fired power you can find, your carbon footprint on an electric bike is still almost too small to measure.  Even better, e-bikes are blast to ride, and they get you across the Hudson River for free!


What are the take-away points for this, if you personally want to lower your carbon footprint?  It’s pretty simple:
  1. Arrange your live so you don’t have to travel as far.  See if you can live close to where you work, etc.
  2. Ride the bus if it saves you time, money or aggravation.
  3. Plan on spending $25K for your next car, which should be a hybrid and get at least 45-50 mpg, even in the city.  This is less than the average $30K spent on new automobiles in America today.
  4. Go get an electric bike, and ride it wherever you find it to be practical.  You will make the money back very quickly in lowered costs of gasoline, wear-and-tear, tolls, etc.
  5. Get involved in your local government to adopt a complete streets policy — on that provides safe bicycle facilities in your town

This article is Copyright (c) 2012 by Bob Fischer and used by kind permission. Unauthorized use and/or duplication of this material without express and written permission from the author is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Bob Fischer and The Jersey Biker with appropriate and specific direction to the original content.


  1. The ratio of 4/1 for fuel calorie use per food calorie between beef and grains sounds low -- doesn't it take more than that just to feed the cattle? The "incredibly inefficient" link suggests as much.

  2. Great article with some interesting and non-intuitive conclusions.

    But I have to take issue with the crazy notion that an electric bike is better for the environment than a conventional, human-powerd bike. Where is the evidence that the banana or cheeseburger you mentioned are ADDITIONAL to what a cyclist would normally consume? North Americans (at least) eat far more calories than they need already, so it's not a given that they would require more if they started biking. I have heard this canard many times, and it always annoys me. I commute by bicycle, and I can tell you from my personal experience that I don't eat more just because I bike. I still need to eat breakfast and dinner! So not only is the author drawing a conclusion on carbon footprints that isn't warranted from the evidence he presented, but he is also advising against a form of transportation that would actually decrease the alarming level of obesity. Not good on either front.

  3. I've sent this round to a few people to get some views, but one initial point: the idea of compaction and smart cities is sort-of commonly agreed to make sense, but it's one of those things that once you include all the factors isn't quite as important as one might imagine. Here's a study by a colleague of mine. Key quote: "Our results reveal that compaction can reduce emission relative to other spatial scenarios but that the differences are small, about 5% between extremes, an order of magnitude less than emission growth observed over the trend period. Form has more influence for settlements where the pattern and proximity of employment, housing, and services can make cycling, walking, and public transport provision more feasible. We conclude that pricing and technology measures offer better prospects for combating the growth in carbon emissions of urban regions, but that the type of urban form delivered is likely to be a significant determinant in the type of clean energy technology that can be implemented."

    A couple of people have also pointed out humans burn ~100W when driving, not zero watts. Someone else has said that even with very carbon intensive UK public transport, it's still a lot less co2 than driving for the same person-demand, but I need to chase that up.

  4. [long and rambling, sorry]

    What about air pollution?

    I'm tempted to look into it, but I know that a proper comparison between the various different emissions profiles of cars, trucks, and electrical power plants would require weeks of work. Maybe somebody's already done it?

    I know that diesel engines like those used in locomotives and buses have very strict emissions limits coming online. How those compare to multiple Prii is beyond me. Lower limits for coal and oil fired electricity are also in the pipeline but being fought bitterly by industry and think tanks ("utility MACT").

    Finally, something about the "food energy" estimates always seems wrong to me. I know that sometimes the truth is unintuitive, but I feel like the estimates for energy use by the agricultural sector are just too high. Using the back of the envelope numbers above, I figure that roughly 1/3 the cost of a loaf of bread (a perishable prepared food product) is just agricultural energy. Plausible, but seems high. If milk has a 10:1 caloric input to output ratio (between beef and grain), the entire cost of a gallon of whole milk would have to be spent on the energy to produce it... somebody's math is wrong (probably mine, honestly). Also, as one of the above posters was saying, does the "energy cost of walking/biking" measure the full energy usage of moving or just the marginal increase in energy usage over resting energy?

    In general though:
    Move less. Share the ride as much as possible. Electrify where possible.

  5. A quick addition...

    Just starting to poke around into agriculture energy.

    Some of the "fossil footprint" studies are comparing inputs for meat vs. vegetable protein and as such are only counting protein, when of course much of our energy comes from carbs as well.

  6. I grew up in New Haven (CT), a small city whose "metro area" is a few hundred thousand. Housing was cheap and not particularly dense, and everything I wanted was within a 5 mile radius of my home.

    Now I live in New Jersey and commute 10 miles to work (by electric bike). Dropping off my kid at school, going to work, and then coming home takes about 30 miles, and someone else still has to pick the kid up. Even in New York City proper, transportation requirements are far greater than where I grew up: Manhattan is over 10 miles long! New Jersey and New York City are both more built-up than New Haven.

    One thing I think we can conclude from this unscientific study is that transportation needs increase with the size of your city, almost no matter what you do. Maybe the "right" low-carbon way to build a megalopolis is as a series of small cities laid side by side --- essentially the LA model.

  7. Good points. However, I think I already mentioned this in the article: that if you're a couch potato, then manual bike is probably the best way to go. I well present the same thing here, with greater detail.

    The Mayo Clinic recommends 2.5 hours of moderate aerobic exercise per week, or to aim for 30 minutes per day. At a typical 10mph, 30 min/day will only get you 5 miles, whereas my round trip commute to work is 20 miles. Biking is also not a comprehensive form of exercise, you probably will need to do something else physical as well.

    I conclude that if your transportation needs are under 5 miles/day, then you can consider biking to be carbon-neutral because you needed the exercise anyway. But beyond that, you need to account for the extra food you eat. Biking has been my main form of transportation my entire life, and I am very aware of the extra food I eat on days I ride my bike --- even the electric bike.

    I bike 20 miles round trip to work, and many days my total distance is closer to 30 miles, probably on the low side for suburban America. My route involves multiple elevation changes of 300ft, and I carry many pounds of stuff I need for the day. That is on top of other exercise I get. All this would not be possible for me on a manual bike, I would have to drive or take the bus instead. Even with the electric, the distances I travel are tiring. Remember that electric bikes ASSIST, they certainly don't push you up hills all by themselves.

    In the end, I don't think we should get too worked up over electric vs. manual bikes. As long as our biking is powered by carbohydrates rather than cheeseburgers, the comparisons cited above show it to have just one quarter the carbon footprint of a Prius, and far lower than riding the bus. If everyone switched to bikes, we would certainly save a lot of CO2 and be healthier to boot.

    But I do stand by my original claim that, overall, for the distances we actually need to travel, the electric bike is the lowest-carbon form of transportation out there.

  8. Well, he did say "If you’re a couch potato and need the exercise anyway, then the bike is a clear winner." but you and dan below are correct to point out that the driver burns calories too and one should only count the actual extra calories one would need from the additional exercise.

  9. Is there any legal distinction between electric bicycles (what you're talking about here) and electric motorcycles (which have mass, acceleration and top speed very similar to a gas-powered motorcycle)? If there is a distinction, how is it drawn? There definitely needs to be a distinction for safety. That said, even the heavier class of bike is an efficiency improvement over a car that has empty seats.

  10. It appears the answers can be more complicated than the question, and vary from jurisdiction to jurisdiction. Here's one answer:

  11. Electric bikes are a new product category that came out of China in the past decade. They are regulated at the National level as a consumer product --- just like a frisbee, manual bike, chain saw, etc. To qualify as a consumer product, they must have functional pedals, be no more than 750W and have a governed top speed of 20mph, after which the power assist cuts out. As a consumer product, they are legal to buy and sell anywhere.

    State laws vary, and they are not street-legal in all states. Many of the laws were written before electric bicycles even existed, and we are left trying to apply gasoline moped laws to bicycles. When state legislatures have looked into the issue, they have concluded that electric bicycles should be regulated as bicycles. In the eyes of the law, they are not "motor vehicles." The key here is the top speed of 20mph, which is about the speed that many athlete bikers ride. No state has ever made a law specifically banning electric bicycles.

    We are working on getting electric bicycles formally recongized in the various state laws. In the meantime, it is rare for electric bicycle users to be harassed by the police, as long as the bike looks like a mountain bike (not a scooter) and the driver is well behaved.

    No matter what the comparative carbon footprint is of an electric vs manual bike, this new class of vehicles offers huge potential to lower our carbon footprint and provide clean, sustainable, personal transportation in the developing world. Lawmakers would do well to accomodate it and encourage its use.

  12. The problem that always puzzles me is the "marginal trip" problem. I think it's pretty clear that for a single trip, getting on a bus or a subway will add less marginal energy use to the system than driving my car. But eventually, everyone getting on the bus for that marginal trip requires adding new service.

    What's a poor boy to do?

  13. Yes, I think this question lurks under the whole article. Public transport (or otherwise shared scheduled vehicles) does have inherent inefficiencies, but they are reduced the more people use them.

    The whole airline business appears to revolve around filling the airplane. It's similar to a network effect (the first telephone is useless, the second one useful in communicating with the first one).

    But we can't charge the whole cost of the flight to the first passenger and consider all the others to be free riders. The question here is whether to consider the cost as per-seat or per-passenger. There are arguments for and against each of them.

  14. If you're using a transit link that's running at or over capacity on any part of its route, then you need to charge that to your carbon footprint. The typical example is you're a morning rush-hour commuter heading into town.

    If you're using a transit link that's mostly empty, then I think it's pretty safe to consider it carbon-neutral. In this case, you are doing your part to increase the seat utilization of the system. The typical example here is you're a reverse commuter.

    If you're using a transit system that's used so little that it never approaches capacity... well, I don't know what to say. Probably still best to charge peak-direction travel to your carbon budget. Because IF people used that system a lot, THEN they would have to add more buses.

  15. Another way to put it is that in New York you have many more opportunities. If you live in New York roughly the way you might live in a town the size of New Haven, you would not have to even get on the subway. You need to compare apples with er, apples of roughly the same value.

  16. What about the per-seat energy cost of constructing the Prius vs the bus? This gets raised sometimes.

    As a start, suppose every penny of the Prius base price were energy costs. $25K. And then suppose it is good for 150 K miles. Then we are spending at most an additional 18 cents per mile. This is a huge overestimate because there are resource, labor, and profit components to the base price. So let's say we are looking at two cents per mile amortized over the life of the vehicle. It's in the noise, even if the construction cost of the shared vehicle is zero.

  17. Numbers I have seen put the estimate of embodied vs. operational energy between 15% and 30%. The higher estimates (22%+, ~30%) are for hybrids. Toyota gets 29% for a Prius but assumes that the vehicle goes less than 100k miles. Less than 100k miles for a Toyota seems pretty conservative to me...

    Rule of thumb, I'd go ~20% embodied emissions for an efficient small car.

    I'm skimming Chester/Hovarth 2009 who have attempted a very comprehensive emissions survey for all kinds of transport, including the infrastructure it runs on. According to their estimates rail does really well across the board (energy, CO2, CO) except electrified rail does poorly in terms of SO2 and diesel rail does poorly in terms of NOx (these problems are easier to solve than CO2). They do not include a hybrid car in their survey. Full buses look great; empty buses are a nightmare.

    Interestingly, airplanes do very well in terms of emissions per passenger/km which leads to the somewhat uncomfortable conclusion that long distance travel is a problem no matter how you do it and future business and holiday travel will have to sharply reduced.

    It reminds me of the surprisingly good assessment of future transport in Monbiot's "Heat." At first I rolled my eyes at his love for highway motor coaches traveling from city outskirt to city outskirt, then realized how close to the mark he was recently as I stood waiting in a long line to board a Megabus in a suburban parking lot.

  18. The other reason for transit systems (apart from fuel efficiency) is congestion. Do you prefer sitting in a train reading the paper (or blogs) or sitting in grid locked traffic looking at all the other cars around? To be sure, if there is no worthwhile transit system, then it's likely the roads will be chocked and you won't have much choice. A transit system hopefully reduces the congestion, although probably it will reach some equilibrium point where the pain of sitting in traffic jams balances the additional time and inconvenience of taking the transit for the average user.

    Similar arguments for the bicycle. Do you prefer sitting in the traffic jam or zipping along unimpressed by traffic (maybe even on a pleasant bike path if your local city has done things right)

    So, it's not only about energy.

  19. No, I disagree, I don't think this is an exception to the rule.

    For example: there are plenty of New Yorkers who commute 30 miles to work. Not many people do that in New Haven. Why would you bother, when decent affordable housing is available so much closer?

    It's easy to suggest that all the opportunities you need in New York are right down the street. Problem is, they're not. Sure, all the supermarkets and drugstores and bars and whatnot that you need are in close by. But not jobs or cultural resources --- where you find yourself traveling a long way into Manhattan.

    In New Haven, everything was 3 miles away. And I mean everything. Unless you live in Manhattan, that is not even remotely possible in New York City. Remember that Manhattan is only for the top 10% in wealth. Queens and Brooklyn are both twice as big, and that's just a start.

  20. I agree. But if we look at pro-transit arguments in the general conversation, many of them come down to energy. We need to be pro-transit for the right reasons. And that right reason, I believe, is to provide mobility in higher-density built environments where congestion is a persistent problem. Transit is a vital part of any reasonably efficient large city.

  21. Pingback: Another Week of GW News, November 4, 2012 – A Few Things Ill Considered

  22. There are a few things that complicate considering of public transit. One of them is that no transit system is designed to optimize energy usage in the first place. There is a lot more they could do, such as employing a wider range of vehicle sizes to match expected ridership, that would improve energy efficiency but make them more complex to run and so probably increase operating costs. Then there's the issue of how different the efficiency is for different users. For a typical transit system, the vast majority of rides happen during a few peak hours, but the majority of vehicle trips happen off-peak. Looking at the average fuel efficiency of a transit system is sure to cause you to underestimate how fuel efficient it is to ride in rush hour in the peak direction, when vehicles are standing room only. But the inefficient off-peak service is necessary to make the service a simple and dependable one, and transit agencies will most likely run as much service as they have a budget for, with actual off-peak ridership affecting where they allocate resources but likely not having much effect on the total amount of service they run.

  23. The facts here demonstrate our inability to change the way we live to even slow, let alone reverse, our fossil footprint and me more now habits. It is too much to expect Americans to stop digging out of our hole, as to do so is "communistic". But I don't see any other way.

    What to do? Irresistible force meet immovable object.

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