How green is public transit? The answer may surprise you

mpg transit use

Brad Templeton looks at the per-passenger cost of taking public transportation vs. other types of transportation (such as cars and bikes) and finds that the greenness of public transportation has been much exaggerated (see chart above).

A full bus or trainload of people is more efficient than private cars, sometimes quite a bit more so. But transit systems never consist of nothing but full vehicles. They run most of their day with light loads. The above calculations came from figures citing the average city bus holding 9 passengers, and the average train (light or heavy) holds 22. If that seems low, remember that every packed train at rush hour tends to mean a near empty train returning down the track.

Transit vehicles also tend to stop and start a lot, which eats a lot of energy, even with regenerative braking. And most transit vehicles are just plain heavy, and not very aerodynamic. Indeed, you’ll see tables in the DoE reports that show that over the past 30 years, private cars have gotten 30% more efficient, while buses have gotten 60% less efficient and trains about 25% worse. The market and government regulations have driven efforts to make cars more efficient, while transit vehicles have actually worsened.

My figures suggest the city bus moves 3,000lbs of bus for every passenger on average, and still 500lbs per passenger when fully packed at rush hour — starting and stopping all the time.

In order to get people to ride transit, you must offer frequent service, all day long. They want to know they have the freedom to leave at different times. But that means emptier vehicles outside of rush hour. You’ve all seen those huge empty vehicles go by, you just haven’t thought of how inefficient they were. It would be better if off-hours transit was done by much smaller vehicles, but that implies too much capital cost — no transit agency will buy enough equipment for peak times and then buy a second set of equipment for light demand periods.

Some cities do much better than others, and some countries do much better than the US:

This Australian Study cites figures saying that Western Europeans use only 76% of U.S. BTUs/pm in their private transport, and only 38% in their transit — 2.5 times more efficient. Rich Asians do even better at transit — they are almost 4 times as efficient in terms of energy/passenger-mile.

Their private transport is better because they own a lot more motorcycles and scooters, as well as smaller cars. Asians do almost 10x as many miles in motorcyles as Americans. Their transit is better primarily because of ridership. They take 5 to 7 times as many transit trips per person. Asian transit actually attains a higher average speed than private travel, another big booster.

They also have much more efficient vehicles.

Note however that in spite of their much higher ridership, transit in Europe is still only 7% of private vehicle energy use, and I would guess about 5% of total compared to ~1% of total for the USA. Even they have the automobile bug pretty strongly.

It’s worth taking a look at:

Brad Templeton: Is green U.S. mass transit a big myth?

Templeton wonders if it might be more worthwhile to push people towards more fuel efficient vehicles. Along those lines it’s worth considering the MPG Illusion.

(via Robin Hanson, who has a considerably less positive view of transit than Templeton)


  1. This article is so fantastically horribly wrong that I’m astounded anyone would repeat it.

    Average ridership is a major factor in fuel efficiency. So is traffic. In a place like the US it isn’t surpising that we see figures like that. Ridership and traffic is directly related to the scale of transit.

    “The figures below are for the DoE’s average passenger loads over the entire USA”

    Look at other countries in Europe and the entire argument disappears in a puff of smoke. People with calculational skills have a serious obligation not to promulgate bullshit like this when they know the critical multiplying factors.

    Light rail with high ridership (like the Luas in Ireland) is thousands of times more efficient than a fully loaded car.

    Shame on Brad Templeton!

  2. Uh, Rowan, did you actually read the article? Europe and Asia are specifically addressed in the second block of text I quoted.

  3. Here are some conclusions I think we can make from this:

    1. Transit is not a cure-all

    2. Transit vehicles need to be held to higher fuel efficiency standards

    3. Motorcycles and scooters are at least as green as transit and should be promoted along side transit as a green alternative to cars.

    4. Walking and biking are greener than transit.

    5. Getting the least-fuel efficient vehicles off the road (SUVs, large trucks) is more important than promoting transit. (This is further supported by the MPG Illusion)

    6. Transit planners should work to improve routes, and consider increasing the mix of transit vehicles (such as using smaller vehicles during off-peak times).

  4. Clearly transit is not as green as we would like it to be. That said, and as Templeton specifically suggests, if transit is running anyway, it will universally be the most green, because it will run with or without you. If you are seeking transportation in a place with public transit, it will always be the greenest option for you as an individual. Thus the ridership issue, and the more than twice as efficient european and asian transit systems. But even then, no gas powered transit system can compete with an electric or human-powered vehicle. If we’re going to reduce our greenhouse gases to the level we need, we need to change our agriculture to use vastly less fuel, get people traveling by electric vehicle, ship our goods by electric train, heat our homes with electricity, and get all of our electricity from renewable resources. The faster we can do this the more stable we will be as a nation throughout this century and beyond, for reasons of peak oil, peak natural gas, and peak coal, not just for CO2 pollution fucking up the planet.

  5. “It will always be the greenest option for you as an individual.”

    I think walking or biking are greener. Although Templeton shows the calorie cost of biking on his chart (and has addressed the calorie cost of walking elsewhere), we need to burn those calories anyway, making your trip carbon neutral. (In other words, it takes extra calories to bike instead of walk, but those calories need to get burned eventually – might as well combine your transit with your exercise.)

    Riding the bus puts a little bit more strain on it, costing slightly more fuel. It makes it more efficient than driving , but less efficient than walking or biking (but only slightly so).

    Anyway, if there’s transit already running, it’s more efficient to take the already-running transit than to take a motorcycle or a scooter or to car pool. My conclusion # 3 needs to be revised.

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