Your CO2 Emissions Per Mile May Vary

Back at ya, Sightline.  There are obvious conclusions to be drawn from the bar chart above, but when the interplay of land use patterns is also considered, the case for transit over cars becomes even stronger.

Since transit typically serves areas with higher levels of density and land use mix, transit trips tend to be shorter than car trips.  One credible commenter noted that in the U.S. the average commute distance by car is 15 miles, while by transit it is only two miles (if anyone has references to related data please comment). Thus compact, mixed-use development enables the double whammy of travel modes that emit less greenhouse gases (GHGs) per passenger-mile, coupled with fewer miles traveled.

And compact development is also essentially a prerequisite for what are by far the two most environmentally benign transportation modes — walking and biking.

As shown in the chart above, rail transit and a bus 3/4 full emit about half the GHGs per passenger-mile as does a Toyota Prius.  Some take this to mean that if we can double the gas mileage of a Prius — which shouldn’t be that hard — then why bother pushing for transit and compact development as a strategy for reducing GHG emissions?

The first and most obvious flaw in the above line of thought is that if we can double the efficiency of a car, then surely we can also double the efficiency of a bus or train.

The second flaw is that we know what happens to per-capita vehicle miles traveled (VMTs) when we build sprawl — they go up.  As noted in the book Growing Cooler, since 1980 VMTs in the U.S. increased at three times the rate of population growth.  Assuming business as usual, i.e. sprawling development, VMTs are projected to rise by 48 percent by 2030.  In this scenario, the average fuel efficiency of our fleet will have to be boosted by one half just to keep GHG emissions from rising above current levels.

The third flaw is that building sprawl not only increases VMTs, it locks in land use patterns that eliminate the possibilities both for transportation modes that are more efficient than cars, and for shorter trip distances.  When roads and parcels are laid out, they persist for hundreds of years.  While there is a severe urgency to address climate change quickly, the problem is not going to disappear in a hundred years, and all indications are that we will need to apply every strategy we can over the long term.

Compared to sprawl, compact development supports a much more balanced range of transportation mode options.  It does not render cars unusable — even in the densest U.S. cities large fractions of the population drive cars.  Meanwhile, transit and density are mutually catalytic and mutually supportive.  And in the U.S, walking and biking as practical transportation are almost nonexistent everywhere except cities with compact, mixed-use land use patterns.

Lastly, compact development and transit have significant benefits beyond the reduction of GHG emissions.  There is no question that improving the efficiency of cars is a strategy we should be aggressively pursuing, and that could yield relatively significant short term results.  But to focus solely on cars while neglecting land-use patterns and alternative transportation modes not only disregards the long-term perspective on climate change, but also ignores the myriad other negative impacts of a sprawling, car-dependent world.

To take but one local example, sprawling development is one the chief causes of the decimation of the Pacific Northwest salmon runs.  But even though that loss doesn’t appear on any accountant’s balance sheet for building sprawl, it’s a significant cost we all pay, whether or not we enjoy the benefits of spacious yards and convenient travel by car.  How many thousand salmon is one McMansion worth?

43 Responses to “Your CO2 Emissions Per Mile May Vary”

  1. Crapola

    I’ve heard that scooters have higher emissions than SUVs. Any data on this, since you’re investigating and all?

  2. justin

    crapola an old scooter does have terrible emissions (like a 60’s vespa) but modern 4 stroke scooters can be quite clean.

    The new yamaha c3 has a 49cc direct injected 4 stroke that burns very clean and gets about 115 mpg.

  3. JB

    The chart doesn’t tell us anything useful about emissions per passenger-mile for cars vs. transit in general. For that, you need to compare the average emissions per passenger-mile for each mode of transportation. Yes, a train or bus that is full or nearly so is much less polluting per passenger-mile than a car with a single occupant. But buses and trains are rarely full. They’re rarely even close to being full. The average load factor of transit buses is something like 20-30%. That is, on average, out of every 10 seats on the bus 7 or 8 are empty, and the bus is burning gas to haul around all those empty seats.

  4. Joshua Daniel Franklin

    JB, “Transit Bus (1/4 full)” is right above “Prius” on the chart.

  5. JB

    Joshua,

    The point is that it doesn’t provide any indication of which level of occupancy is typical or closest to the average for each mode of transportation. Yes, “Rail transit (50 riders per car)” is much cleaner (per passenger-mile) than a Prius with a single occupant. But how often are trains that full? And how often do Prius’s have only a single occupant?

  6. JB

    The first and most obvious flaw in the above line of thought is that if we can double the efficiency of a car, then surely we can also double the efficiency of a bus or train.

    I don’t know how you think that follows. In general, new technology to increase the efficiency of cars can also be applied to transit motor buses. And, indeed, transit agencies are already running substantial fleets of hybrid-electric buses and buses that run on natural gas (which is much cleaner than diesel fuel). One big exception to this might be plug-in hybrid technology. It will be difficult to take transit buses out of service for the long periods necessary for battery recharging without incurring extra costs. Even if bus efficiency can be improved to the same degree as car efficiency, buses are barely competitive with cars now, so this won’t change the equation much.

    As for rail, almost all urban rail transit already benefits from the efficiencies of electrical propulsion using centrally-generated electricity. What new technologies do you see on the horizon for improving the efficiency of light rail and subway systems to a degree comparable to the improvements in car efficiency promised by hybrid/plug-in hybrid/hydrogen technology?

  7. kent

    JB – The Amtrak trains are usually pretty full, I’d say 90+%. I ride to Portland frequently and this is a pretty solid observation. Remember they only hook up as many cars as needed for the tickets sold. Unlike a bus they can change capacity on the fly for every trip.

  8. JB

    kent,

    According to the most recent data from the Bureau of Transportation Statistics, whose source is Amtrak’s Monthly Performance Reports, Amtrak’s passenger load factor for November 2008 was slightly more than 50%. Load factor is defined, more or less, as the fraction of seats that are actually occupied by passengers. So a load factor of 50% means that, on average, half the seats were empty.

    See:

    http://www.bts.gov/publications/key_transportation_indicators/november_2008/html/rail_passenger_load_factor.html

  9. Joshua Daniel Franklin

    JB, that’s overall Amtrak and Kent is referring to the popular Seattle-Portland route (Amtrak Cascades or part of the Coast Starlight).

    I agree with your earlier observation that these data become more useful when combined with patterns of movement. That will help plan to meet the needs of current and future employees and residents.

  10. r

    Forgive my ignorance but how exactly do i emit Co2 while walking?

  11. JBB

    JB- For what it’s worth, actually, plug in electric-hybrid and fully electric technologies could be very applicable to buses. Remember, most transit systems need the most capacity for just a few hours each AM and PM peak; during mid-day, they have buses sitting around their lots. They could easily use electric technology for these buses since they are only on the road for a few hours at a time and can charge over the mid-day period.

    And in fact, such buses are already available from a company called AVS, although my impression is that their reliability has been not so great.

  12. dan cortland

    Not listed are hydroelectric-powered transit buses (trolleys) such as Metro’s that have much lower footprints than diesel buses.

  13. dan cortland

    r@10: you exhale CO2, as long as you’re breathing. (Your cobalt emissions are mysterious.)

  14. Steve

    Couldn’t you correct for the relationship between driving and sprawl by graphing average emissions per person-commute rather than per person-mile?

  15. dang

    JB – Your observations are good and I assume supported by data (please provide a reference for the 25% figure you cite as I would like to understand its context), but I believe Dan is making a point that you seem to be missing. It’s not about business as usual, and it definitely should not be so focused on the means (or ridership) of transit as much as it should be on land use patterns and how those patterns accommodate greater efficiencies and the transit systems that can achieve those efficiencies. Building denser will provide more viable options and reduce the distance of all trips. Carpooling dramatically cuts per person emissions as would doubling the efficiency of a Prius.

    But… if land use patterns continue to provide few options, require greater distances to be traveled and funnel more people onto roadways, I would hazard a guess that the efficiencies gained are in time reduced or lost entirely. Transit operating at 1/4 capacity is not desirable, but if it were to double it would provide a significant reduction in GHG emissions by the data provided above.

    Beyond that data above though, when considering the items I presume are not fully accounted for above–GHG emissions generated in the production of vehicles and the infrastructure required to support them and their overall impact on the ecology and society (think more immediately about impervious surfaces, storm sewers, water treatment requirements, heat island affects, reduced vegetation and compromised ecosystems; and in a broader context, fuel production and the means with which that production is secured)–carrying on as usual generates significant liabilities now, that only become more severe in the future, when pursuing other options becomes more complex and costlier to implement especially when the timing of our patterns seems to be most critical at this moment.

  16. jeff

    I’m a reverse commuter. I pollute less than 1/2 what a normal commuter would. I also have more time to enjoy my life. Do I wish my employer would move downtown? Yes, but then they probably couldn’t afford to hire me.

    Is it their fault they prefer suburban life? no. Would a bus in suburbia help? no, buses sit in traffic to. Would a train help? no, that would be stupid to put a train out here.

    This chart is pointless and doesn’t really do anything for me. why don’t you just go out and say “let’s nuke suburbia” and stop hiding being phony graphs.

  17. JB

    JB- For what it’s worth, actually, plug in electric-hybrid and fully electric technologies could be very applicable to buses. Remember, most transit systems need the most capacity for just a few hours each AM and PM peak; during mid-day, they have buses sitting around their lots.

    There already are some all-electric trolley buses (in San Francisco, for example). But they require overhead power lines that are expensive, unsightly and inflexible. The dominant form of transit bus is likely to remain the transit motor bus. The maximum all-electric range of a plug-in hybrid transit bus would be unlikely to exceed 40 miles. That is probably less than a single roundtrip traversal of the average transit bus route. To continue operating in all-electric mode, the bus would then need to be taken out of service for battery recharging. PHEV might make sense for some vehicles and services with very limited hours of operation, but for general transit bus services it just doesn’t seem to make economic or practical sense. I’m not aware of a single U.S. transit agency that has plans for PHEV buses.

    In any case, the broader point is that buses are already barely competitive with cars on energy-efficiency and emissions per passenger-mile and new technology isn’t likely to make buses any more efficient relative to cars.

  18. JB

    dang,

    The seating capacity of a standard U.S. transit bus is about 40. The National Transit Database reports the average transit bus occupancy as about 10 passengers (passenger miles traveled per vehicle revenue mile). So, on average, about three-quarters of the seats on a transit bus are empty. It’s actually even worse than that, because additional fuel is consumed driving empty buses to and from the bus depot for storage/maintenance/refuelling at the start and end of each day of service. See:
    http://www.ntdprogram.gov/ntdprogram/pubs/NTST/2007/HTML/Operating_Costs_and_Performance_Measures.htm

    As for land use, there is very little realistic potential for achieving meaningful reductions in energy consumption and emissions through “compact development” and other forms of densification. The sheer scale of the transformation in land use patterns that would be required is prohibitive. It’s all very well saying that we could dramatically cut our energy use as a nation if we all agreed to live in small condos in high-rise buildings, work and shop close to our homes, and do most of our traveling by public transportation or by walking/bicycling rather than by private car, but most Americans are simply not going to live that way. I discussed this in greater detail in comments to an earlier post.

  19. jeff

    JB JB JB JB, ahh it’s so funny, because you don’t recognize where the spending is going to be coming from. The spending is mainly coming from the new creative class, which lives in dense areas close to art and educational scenes. Wake up, we’re living in a country ruled by the creative class, not the blue collar or agricultural class anymore. If you think that commute times don’t take a toll on families then I wonder about yours.

  20. jeff

    Check out the book “The Rise of the Creative Class”. People just can’t live in the suburbs and achieve anything out of life without massive suffering.

    JB, suburbs don’t just appear out of nowhere in the middle of the country, they are usually surrounding a big city, and the suburbanites want those amenities.

    How do you propose to tackle congestion and time wasted on the road? what’s your solution? You sound like an isolationist.

  21. JB

    Jeff,

    Average commute times increase with density and decrease with sprawl. One of the big benefits of sprawl is that tends to reduce travel times.

    Not sure what you mean by the “creative class,” but for many decades jobs of all kinds, including highly-skilled knowledge-indsutry jobs, have been migrating outwards from central cities to the suburbs along with workers. Most commutes are now suburb-to-suburb or intrasuburb rather than suburb-to-central-city.

  22. Astroturf-warrior

    JB,

    You’re clearly trolling (astroturfing) in from somewhere else. This is a Seattle-based blog. We know all about electric trolley-buses; you see, Seattle is full of them.

    Many of the highest-volume lines are trolley buses, and their “inflexibility” is a good thing. They encourage ridership by following predictable paths. Nothing turns off new users to a transit system than random reroutes. You know with a trolley bus that it’s not gonna take an unexpected right, hop on a freeway, and end up in Crackton just because you got on the 22A instead of the 22.

    Please do go away and spread your Builders Industry propaganda elsewhere.

  23. JB

    Wikipedia has a good entry on trolleybuses, including a description of their advantages and disadvantages over motor buses.
    http://en.wikipedia.org/wiki/Trolleybus

    The use of trolleybuses appears to be declining.

  24. Joshua Daniel Franklin

    Yes, that “San Francisco, for example” is really a giveaway that JB knows nothing about Seattle. To predict the future, I’d say rising energy costs and flatlining road funding will very likely lead more Americans to “work and shop close to our homes, and do most of our traveling by public transportation or by walking/bicycling rather than by private car.”

  25. kt

    Suburbs are an outcome of the automobile and economic divisions. Admittedly, there were ’streetcar’ suburbs even in the 1800s, but the suburbanzation of America started in earnest with the adoption of the automobile as the preferred means of commute. This was and is subsidized in the form of roads and infrastructure.

    We have been through a few iterations now. There are still original discrete towns that pre-exist the auto that served as local centers. We have the rise of large cities. We saw the decline of those cities as nice places to live, along with the rise of suburban communtities. After WWII, suburbs became largely places the Mom and kids had the good life while Dad commuted to the city. They were much denser than what we see now, walkable and had their own commercial life. Bad part was they did not have mass transit. Good part was a lot of people could walk to stuff, and driving to the grocery store was a matter of driving one or two miles instead of the long trips we now take in Seattle to the Costco (or Renton or Bellevue).

    Of course I am ignoring the reality of anyone either very rich or very poor in this picture.

    Then we see the attempts to make center cities ‘great places’ to live, more mass transit systems that all go downtown, but at the same time much more suburban building of office parks, strip malls and subdivisions where 4000-5000 sq ft homes are not uncommon.

    This sort of regional and national development has continued well past it’s ’shelf life’, especially when all parents are commuting hither and yon, separated from thier home life. Even considering that families are smaller or people are just not having children, commutes are further and longer.

    It just makes me cringe that builders have gotten away with building 5000sqft homes for childless couples in the last 20 years where we used to have farms. And, jurisdictions happily build the roads. This is true everywhere. It’s particularly disgusting to see a brand new road go for miles and miles past farms to a new subdivision. And, those people believe they now live in the country. It just happened to be a farm that some developer bought and got the locals to agree to rezone and build a road.

    There are ways with land use laws and taxes that would stop this stuff. But, these laws need to supecede jurisdictional interests. Bad news is that it should have been stopped a long time ago. If we took the word development out of our vocabulary, maybe developers would not have a place at the planning table.

    Now we talk about buses versus rail and try to guilt people about where they live. The point is that we need to STOP building in places that are not built, and we need to dense up suburban towns. Turn that office park into multi-use. Turn that 5000 sqft home into a home for two households. For example, my sister is putting four generations into her house since she hated it when her husband unilaterally decided that they had to have the huge house, but she is just skirting the legal side of her zoning laws. Work with where we have built, infill retail where people live and houses where we work.

    Will we be driving and needing mass transit? I believe both will be true. Can we be driving less distances on a regular basis and using more transit between these nodes? As long as we STOP building in new places, otherwise all other discussion is futile.

    By the way, the amount of infill we need is to support about 1% more people per year based on the info I saw that King County grew 10% since 2000. That does not require a huge tear down-build new effort IMHO

  26. JB

    Yes, that “San Francisco, for example” is really a giveaway that JB knows nothing about Seattle.

    I know quite a bit about Seattle. But I’m not sure why you think any of the arguments I have been making depend on knowledge of Seattle in particular, anyway.

    To predict the future, I’d say rising energy costs and flatlining road funding will very likely lead more Americans to “work and shop close to our homes, and do most of our traveling by public transportation or by walking/bicycling rather than by private car.”

    Well, maybe, but not on the scale needed to make a meaningful difference to CO2 emissions. We went over this in another thread. And so far, there’s no real evidence of any trend towards higher density. Most of the growth is occurring in car-oriented suburbs.

  27. dan cortland

    Looks like Metro runs about 159 trolley buses, see here and here.

  28. Joshua Daniel Franklin

    JB, this is a blog about urban planning in Seattle. Reasoned arguments (not just contradiction!) based on national data certainly have a place here, but so does knowledge of a city’s installed transit. It will take a lot of creative ideas for existing infrastructure including suburbs to be integrated or retrofitted into something that provides a real solution to climate change. We cannot rely solely on trends of the present any more than simply look at the chart above and say, “Well, we should all walk or bike.”

  29. Jeff

    Maybe when looking at the present you have a valid point to look at averages across the US to compare CO2 emissions of commuters. It’s a simple fact that suburbanites make up a very large chunk of the pie in the present, so mass transit statistics are of course going to be skewed, especially in county areas with buses which get federal funding to start their systems. However, you’re not looking at the fact that a suburban area with office buildings is EASILY abandon-able, and you’re not looking at trends that city planners know about which I will discuss. Yes, you will see some high tech and knowledge-specific companies in these areas, but my belief is that in the past 10 years there’s been a value change among workers that will continue, in which people will no longer move somewhere just for work, they will migrate towards places with both the infrastructure for entrepreneurship to thrive, and also a community of high culture.

    People who are retiring will still love their suburbs, and I am fine with that. But I can’t imagine those people as the working commuters of the next few decades.

  30. dan bertolet

    JB@6: Congratulations for finding a flaw in a blog post! I may have to fire my editor. Yes, you are correct that it would be more challenging to increase electric train efficiencies. However, I would add that if we made it a priority we’d likely find a way. And we may soon have fast-charging batteries that could be used for bus hybrids:

    http://www.sciam.com/article.cfm?id=better-battery-lithium-ion-cell-gets-supercharged

    As for converting the auto fleet to electric cars, where do you think all that extra electricity is going to come from, especially considering that peak oil and GHG regulation will be putting an ever tighter squeeze on generation? And hydrogen hybrids — really? Last I heard it takes electricity to make hydrogen, or you strip it from methane (a.k.a. natural gas, which we are running out of) in a process that releases CO2. Fuel cells may be efficient, but supplying the hydrogen, not so much.

    And yes, as you claim (over and over), based on current average ridership in the U.S, buses are only about 1/3 more efficient per passenger-mile than the average car. But why do you assume this trend is frozen forever in time? Compact development will lead to higher ridership. We don’t even need to improve the mechanical efficiency of buses to get big improvements — going from 25% to 75% full buses would triple the efficiency. There are many ways we be more efficient running transit and capture more riders — we basically suck at transit in the U.S. cause we’ve never tried very hard. Compact development addresses the root of the problem: it enables shorter trips, and travel modes that are inherently more efficient than an SOV.

  31. JB

    Joshua,

    JB, this is a blog about urban planning in Seattle.

    This post is not about Seattle. It’s about CO2 emissions from different modes of transportation. The other posts I have been commenting on are not about Seattle specifically, either.

  32. JB

    JB@6: Congratulations for finding a flaw in a blog post! I may have to fire my editor. Yes, you are correct that it would be more challenging to increase electric train efficiencies. However, I would add that if we made it a priority we’d likely find a way.

    I see no technologies on the horizon to improve electric train efficiencies to anything like the degree that hybrid, plug-in hybrid and other new automobile technologies have the potential to improve the efficiency of cars over the next 20 or 30 years. Furthermore, since we do virtually all of our traveling by car and very little by electric train, improving the efficiency of cars provides vastly greater potential for reducing energy consumption and emissions than improving the efficiency of electric trains. Cars provide more than 95% of passenger-miles of surface transportation in the United States. Electric trains, far less than 1%. Why on earth should we make improving the efficiency of electric trains a priority when the potential savings from such an improvement are so tiny?

    As for converting the auto fleet to electric cars, where do you think all that extra electricity is going to come from, especially considering that peak oil and GHG regulation will be putting an ever tighter squeeze on generation?

    From the same sources it comes from now, but hopefully with a greater share coming from cleaner and renewable sources. I don’t understand the point of the question. Whether we’re traveling by electric cars or electric transit, the electricity is going to have to come from somewhere.

    And hydrogen hybrids — really? Last I heard it takes electricity to make hydrogen, or you strip it from methane (a.k.a. natural gas, which we are running out of) in a process that releases CO2. Fuel cells may be efficient, but supplying the hydrogen, not so much.

    Not hydrogen hybrids. Hydrogen-powered electric cars that use fuel cells to convert the hydrogen into electricity. The cars themselves will produce zero pollution. The hydrogen will probably be centrally-generated through a process that is much cleaner than burning gasoline in car engines, and then transported to fuel stations. At least, that is the idea. Most analysts seem to believe that hydrogen is the long-term future of automobile technology. But perhaps it will be superadvanced batteries instead. Or something else. We don’t know at this point. For the near-term future, new auto tech will probably be dominated by hybrid and plug-in hybrid systems, and perhaps biofuels.

    And yes, as you claim (over and over), based on current average ridership in the U.S, buses are only about 1/3 more efficient per passenger-mile than the average car. But why do you assume this trend is frozen forever in time? Compact development will lead to higher ridership.

    Higher ridership is not the same thing as higher efficiency. Efficiency is a matter of the distribution of demand, not the total amount of demand. As long as demand continues to vary dramatically across different bus routes and route segments, and across different times of the day and different days of the week, efficiency will be limited. And we’ve been over the issue of compact development in another thread. It just doesn’t offer any realistic potential for meaningful reductions in our total energy consumption and emissions.

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