Housing Complex

Metrobus: The Least Green Big Bus Network in America?

The Atlantic Cities has a good piece today debunking the fashionably counterintuitive notion that cars are in fact greener than public transit. But buried in there are some figures from a 2009 Federal Transit Administration report that paint D.C. in a not-so-favorable light.

Take a look at this chart from the report:

Of the 10 largest "directly operated" bus systems in the country (as opposed to privately operated systems, which account for only 14 percent of bus passenger miles nationwide), the D.C. area's Metrobus comes in dead last in terms of pounds of carbon dioxide emitted per passenger mile. In fact, Metrobuses emit more carbon dioxide per passenger mile (.782 pounds), on average, than the general car trip emissions rate of .59 pounds (though considerably less than the average single-occupancy car trip rate of .96 pounds).

What accounts for this? A large part of the answer is ridership: Metrobus is in a three-way tie for last place in average percentage of seats full, at just 23 percent. When buses are full, they're much greener than cars. But as the Atlantic Cities piece points out, buses don't just aim for eco-friendliness; they also provide a service to poor, underserved areas, where ridership may not always be high but the need is greatest.

Still, Metrobus is among the worst performers in terms of vehicle carbon efficiency. Its buses emit .182 pounds of carbon dioxide per seat mile regardless of ridership, higher than all of the other top 10 bus networks except for Chicago, Philadelphia, and Miami, and much higher than King County, Wash.'s .118 and Minnesota Metro Transit's .122.

And it's not limited to buses: According to the FTA report, WMATA is also a lower-than-average performer in the heavy rail department:

A WMATA spokesperson responds to the below-average emissions performance numbers:

On bus, the main difference is ridership. To calculate the CO2 per passenger mile, the denominator is ridership. Lower ridership = higher lbs. We’re at 0.7 lbs CO2/passenger-mile, and many of our peers are 0.5. Our average load is 11-12 passengers, our peers are 13-18. Our deadheading, average speed, and fuel efficiency are basically normal.

On rail, a lot of the difference has to do with our local utilities, and is not a reflection on Metro. Pepco and Dominion, like the rest of this region, rely on a lot more coal than utilities in other parts of the county.

But before you despair, take comfort: When it comes to traffic safety, D.C. is tops in the country. Our 3.97 traffic deaths per 100,000 people are not only fewer than any state; they're one-seventh of the deaths in the most dangerous state, Wyoming.

Update: The response from WMATA was added after this post was published.


  1. #1

    I would think that seat-miles are a unit unfavorable to the Metro rail system (and possibly also to Metrobus as well) -- with those long connections to the suburban park-and-ride terminals, a disproportionate number of miles are accounted for by legs that are traveled at high average speed but with few passengers. I know it would be hard to determine from the data set, but a per-trip or even per-station basis seems more useful.

  2. #2

    I didn't think the Atlantic article was particularly compelling. Basically it turns out that, at average passenger loads, there's no net carbon benefit to bus transit versus private cars. Even modest gains in personal auto fuel efficiency would cause personal auto transit to be the "greener" choice. In a sense that's good news since most people will continue to rely on cars anyway.

  3. #3

    @JM - you're wrong, because the transit agency is already running the buses. It's not like they are going to cancel 1/10th of a bus trip if you decide to drive.

  4. #4

    JM, even if that's true, I think manufacturing cars for those who currently don't own them would be pretty resource-intensive. Increasing transit ridership would help make the carbon per passenger numbers better for buses and trains.

  5. #5

    sbc - actually the Atlantic article did address "full lifecycle" carbon emissions (3rd graph). For average 9 persons per bus (just slightly below the average of 11), the carbon emissions between bus transit and a sedan are about the same. Again, a lot depends on the size of the car you drive, but auto efficiency is increasing.

    Matt D - huh? That's an odd argument... if everyone stops riding the bus then presumably they won't run as many.

    Don't get me wrong - there are certainly co-benefits to bus transit, such as reduced traffic and reduced land use pressure for sprawl. But the data in the Atlantic article don't indicate that carbon is one of them.

  6. #6

    Why doesn't Metro change electric generation providers? I switched to a low-carbon alternative. Why can't Metro?

  7. #7

    Adam L,

    I don't think this report audits where transit authorities buy their power, but rather it just notes a) how much power they use, and b) what the GHG profile of the power supply in that region of the US is.

  8. #8

    JM - if the priority is to minimize transit GHGs, instead of eliminating all buses, or 10% across the system, wouldnt the best thing be to eliminate the service at the times and places with the lowest ridership, when there are almost certainly well under 9 riders on a given bus?

    Of course the people who tend to ride those are not people in position to use a car - sometimes they arent even physically able to drive, etc. Some bus service is provided as essentially a social service and has little to do with GHG's. Its like asking if meals on wheels is energy efficient. Jarrett Walker has addressed this fairly extensively.

  9. #9

    One other item to consider - the eGRID data that is cited is likely taken from the 2007 version that EPA published (in late 2007 or 2008), which provides information based on data tabulated for 2005. So the numbers are way out of date, and a lot higher than numbers you would see for 2010 or 2011 or 2012, with the rapid increase in renewables and the switch from coal to natural gas electric generation in many areas of the country.

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