Last night I came across an interesting post on which discusses the question of “how green (environmentally friendly) is public transport?” The post responds to the claims that empty buses that operate during off-peak times are likely to counter-balance any environmental benefits that public transport provides over cars during peak hour. It quotes an article in Canada’s National Post:

“Subsidized transit is not sustainable by definition,” says Wendell Cox, a transport policy consultant in St. Louis, and former L.A. County Transportation commissioner. “The potential of public transit has been so overblown it’s almost scandalous.”

It’s not that environmentally minded transit promoters are being dishonest when they argue that city buses are more efficient than private cars: It’s that they’re talking about a fictional world where far more people ride buses. Mass transit vehicles use up roughly the same energy whether they are full or empty, and for much of the time, they’re more empty than full.

For the bulk of the day, and on quieter routes, the average city bus usually undoes whatever efficiencies are gained during the few hours a day, on the few routes, where transit is at its peak.

Jarret Walker, who runs, has a variety of responses to this claim.

In 19 years as a transit planning consultant, I’ve studied the operations of at least 100 bus and bus+rail systems on three continents, and I have never encountered one whose overriding goal was to maximize its ridership. All transit agencies would like more people to ride, but they are required to run many empty buses for reasons unrelated to ridership or environmental goals. To describe the resulting empty buses as a failure of transit, as Cox does, is simply a false description of transit’s real, and conflicted, objectives.

If public transit agencies were charged exclusively with maximizing their ridership, and all the green benefits that follow from that, they could move their empty buses to run in places where they’d be full. Every competent transit planner knows how to do this. Just abandon all service in low-density areas, typically outer suburbs, and shift all these resources to run even more frequent and attractive service where densities are high, such as inner cities. In lower-density areas, you’d run only narrowly tailored services for brief surges of demand, such as trips to schools at bell-times and commuter express runs from suburban Park-and-Rides to downtown. If you do such a massive shift of resources, I promise your productivity (ridership per unit of cost) will soar, and you won’t have as many empty buses.

Why do we know that’s the answer? Because if you rank a transit agency’s lines by productivity (riders per unit of cost), the top ranking services are almost all in one of these categories: either (a) all-day high-frequency service to areas of high density or (b) peak-only commuter express from suburban centers to downtown, or (c) services to suburban schools at bell-times.

So if we were talking about Seattle’s King County Metro area, for example, a ridership-maximizing service plan would probably offer no all-day transit service outside the City of Seattle except for links to the densest suburban centers such as downtown Bellevue and perhaps some older, denser inner-ring suburbs such as Renton and Burien. Beyond that, the suburbs would have nothing but school services and express buses to Seattle at rush-hour. In the dense urban fabric of Seattle, on the other hand, you’d have buses or streetcars every three minutes on every major street, with lots of rapid-bus overlays, etc, etc.

The outcry would be tremendous, the politics toxic, the prospects for implementation zero. I would never propose it. But there’s no question that such a service change would dramatically increase ridership, dramatically reduce the number of empty buses, and thus improve how transit scores on the kind of tally that Cox and his allies propose.

Meanwhile, back in the real world, transit agencies have to balance contradictory demands to (a) maximize ridership and (b) provide a little bit of service everywhere regardless of ridership, both to meet demands for ‘equity’ and to serve the needs of transit-dependent persons.

One analysis that I’ve done for several transit agencies is to sort the services according to whether they serve a “ridership” related purpose or a “coverage” related purpose. Ridership services are justified by how many people ride them. Coverage services are justified by how badly people need them, or because certain suburbs feel they deserve them, but not based on how many people ride. I encourage transit agencies to identify which are which. Once a transit agency can identify which of its services are trying to maximize ridership, you can fairly judge how well those services are doing in meeting that objective, including all the environmental benefits that follow. Until then, the Cox argument is smoke and mirrors.

Overall, I think the point Jarrett is making is that public transport could be far more green than driving, if that was all it needed to be concerned about. Of course that is not possible, as off-peak services are necessary in low-patronage areas so that everyone has accessibility to at least a basic level of service. It’s a good question as to whether we really need a 50 seat bus to provide that sort of service, when it’s likely the bus will be operating mostly empty for its run, but unless we want to abandon any sort of public transport for big chunks of the city it’s rather inevitable that there will be very low patronage routes.

But does that mean public transport isn’t green? I think the answer is potentially, and I’m not sure whether Jarrett’s response really does answer that question – instead somewhat bypassing it. At a fundamental level it seems as though public transport should be more environmentally friendly than driving – as one engine shifting a number of people just has to be more efficient than a pile of engines each shifting one person (and a tonne or so of metal too). Once you throw electrified public transport into the mix the benefits become extremely obvious – but even if we’re talking about diesel buses (which provides the bulk of Auckland’s public transport) it would appear as though public transport is more environmentally friendly than driving. But what about all the empty runs during the middle of the day? What about the fact that peak time buses often travel empty into the city or out of it, only picking up passengers along half the distance that they actually travel? What about the distance buses have to travel from their route to their depot? All of those add up to suggest that each actual bus service probably needs a reasonable number of passengers (an average of 7 I have heard) to make it more environmentally friendly than driving.

So perhaps we shouldn’t simply “bypass” this question about how green public transport is, but actually think about ways in which to improve the environmental friendliness of the system. Do we really need full-size buses to operate inter-peak or late-night routes is an obvious question, while another is finding ways of actually increasing average patronage per service, while not losing ‘coverage’ – which probably includes my pet project of improving cross-town routes so that the efficiency of the system can be increased. Electrifying the rail system will create some significant environmental benefits, as would running electric trams where appropriate – like I proposed for the Dominion Road corridor. Investment in hybrid buses (which I believe is happening) could also improve the environmental friendliness of public transport – and as a guess I think the uptake of hybrid/electric buses will be a lot quicker than the uptake of hybrid/electric vehicles. So there’s certainly a lot that could be done to improve things – perhaps more easily than reducing the environmental impact of individual cars I might suspect.

Another matter which I think is important to analyse is how each additional user of either public transport or a private vehicle has an impact on the environment. Each extra person driving adds additional environmental impact – through more CO2 emissions, other air pollutants, noise pollution and so forth. On the other hand, if we’re providing public transport for reasons other than their environmental benefit, each additional user just results in the existing capacity being used more efficiently, while the environmental effect of the additional car user is avoided. I suppose that if we attract enough additional public transport users we might need to increase service provision levels (leading to a greater environmental effect) but by then our buses are very full so that issue isn’t relevant. If that explanation seems complex, think about whether you’re going to catch the bus or drive tomorrow – if you drive you will pump out more pollution into the world from your car than if you didn’t, while the bus is still going to run regardless of whether you choose to use it. If you catch the bus, you don’t create that pollution from your car, and you ensure that the pollution from your bus is split across more people – thereby being less  ‘per capita’.

Therefore, even if public transport isn’t particularly environmentally friendly, the only way to make that situation better is to improve the service (preferably through better quality/higher speed services rather than more of them) so more people use public transport. If you reduce investment in public transport, and instead focus your money on building more roads, the environmental outcome is inevitably going to be worse – because you still need to provide the PT, it’s now used even less and you have a whole pile more cars on the road.

There are a couple of excellent comments on the post, which sum things up quite nicely. First, by someone called “Allan”:

This is crap. The point should be… there’s a seat for you, and if you take it there is no extra emissions for you riding (virtually), however if you drive you’re polluting a ton. So ride the bus if you care about the environment. You should be looking at your personal carbon footprint not the system’s.

And another by “Russell in Cincinnati”:

But maybe the easiest way to see past the “transit isn’t green” line is with an occasional whiff of reality. 800 gallons of gasoline are consumed by the average resident of Atlanta, in one way or another, cars/trucks/whatever, every year. In Barcelona that number is about 50 gallons. What will the long term consequences be to the lives of Atlantans when gas reaches 10 dollars a gallon, compared to the impact on daily life and housing patterns in Barcelona? Those simple numbers make the gasoline deniers’ handwaving sound like a very small voice, at the bottom of a quite deep beer mug.

Yes, quite. Of course this means that “land-use planning” matters too, which just proves once again that you can’t separate land-use planning from transportation planning (which of course is what the reforms of Auckland’s local government are exactly going to do…. sigh).

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  1. Wendell Cox, hey? I know I should do better, but I knee-jerk reflex sit on the opposite side from everything that person comes down on.

    Doesn’t help that he’s been known to pick and choose statistics to suit his views, as a New Zealand Herald article about his consultancy some year or two back said quite succinctly (basically they came to the conclusion that he cherry-picked data from all over the US to get to his “Metropolitan urban limits are bad for houses prices!” statement, which is the bastard twin of his “PT is bad!” argument).

  2. Yes I am always suspicious of anything he says. Same with NZ’s version of him – Owen McShane. However, I think it is necessary to confront these critiques (whether they are of smart growth or of public transport) as people like Mr Cox and Mr McShane have a surprising amount of political clout. Also, some people write off anything Paul Mees says, whilst I’m a big fan.

  3. Nice post jarbury an interesting read. In relation to land use patterns – according to this study:
    Detroit is where it’s at, and seem to really be managing their growth and transit planning well – little wonder peope are flocking to the city!
    Perhaps in a few years we may be even more like them, certainly we wouldn’t want to end up like Vancouver which tops this list of badly ‘overplanned’ cities. Smart growth is so passe don’t you know. I hope National read this report, Roger Douglas’ lobby group for city planning use it as a guide on what Auckland is doing wrong.

  4. Does it actually matter if public transport is more “green” than private car use? People in large cities overseas don’t use PT because it’s “green,” they use it because it’s the best option for them. In Auckland the best option is using a car, but it doesn’t need to be: trains can be faster and more convenient than cars in many ways. We’re not going to solve climate change by taking the bus instead of the car, so I don’t really think it’s worth worrying about PT’s green image or lack thereof.

  5. The issue of “empty busses” is sometimes raised. When I wander down to (for example) Fanshawe Street shortly, I can be fairly sure that the majority of the tarmac is not being used. If I wander out to my front gate most evenings, what is a busy road on the shoulders of the day is typically under utilised. The volume of public money in land to supply under utilised roading and the resources put into maintaining shoulder-capacity tarmac is rarely raised when the odd empty bus is being pointed at.

  6. Are they really buying hybrid buses? They put it off a few years ago, but the relative price has probably come down since then.

    I think the answer to this question is: public transport can be much greener – if it is given the chance to grow properly.

  7. I think the Link buses are hybrids, but don’t know about any others. Designline, the NZ company who make a lot of buses (and export most of them) have apparently been making many many more hybrid buses recently.

    sj, I agree that “green-ness” does not have to be the prime justification for public transport investment. It is a useful addition though.

  8. I’m sure there is plenty of work on this. The first study that I can find on google comes from Ireland and looks at the carbon output of cyclists as compared to motorised transport: Conor Walsh et al A comparison of carbon dioxide emissions associated with motorised transport modes and cycling in Ireland. The table below tells the story (all numbers are kg CO2 Pass km−1). Cycling is the best, followed by public transport followed by private motorised transport.

    Emissions at max occupancy Emissions at normal occupancy
    Mode Direct Indirect Total Direct Indirect Total
    Cyclist 0.005 0.0061 0.011 0.005 0.0061 0.011
    DART 0.011 0.0006 0.011 0.028 0.0006 0.029
    Intercity bus 0.015 0.0006 0.015 0.029 0.0011 0.031
    Dublin bus 0.016 0.0008 0.017 0.032 0.0017 0.034
    City bus 0.025 0.0015 0.027 0.050 0.0031 0.053
    Private car 0.042 0.0103 0.052 0.120 0.0293 0.149
    SUV 0.052 0.0162 0.068 0.184 0.0579 0.242

    (apologies for the formatting…)

    Of course, carbon output is only one element of green – I’d be pretty surprised if public transport weren’t lighter on the environment than private motors in terms of other types of pollution and ecological impacts.

  9. My understanding is that the hybrid designline buses actually use a gas turbine that is always spinning and charging a generator even when the bus is stopped, this powers batteries that in are in turn used to power the motors. This is obviously different from a standard internal combustion engine or a standard hybrid currently in cars where at low speeds batteries are used and at higher speeds an engine is used. They are definitely quieter than a standard bus and probably much more efficient.

  10. Just in case you are having problems reading that table, the main column to look at is the last in each row: it says that in Ireland, at normal occupancy levels, the total CO2 emissions (measured in kg of CO2 per passenger kilometre) are Cyclist 0.011, DART 0.029, Intercity bus 0.031, Dublin bus 0.034, City bus 0.053, Private car 0.149, SUV 0.242.

    The authors of that paper conclude: All forms of transport have an impact on the environment, either directly or indirectly. Even activities such as walking derive their energy from food produced using fossil energy. At peak times cycling has the lowest direct emissions per passenger kilometre but this differential increases significantly outside these times. DART transport at peak times provides the lowest direct combustion estimate. When the overall emissions, including the indirect emissions from manufacture are included, it is possible that the emissions of cycling may equal those assigned to DART passengers. While transport by private vehicles is the most energy intensive transport mode, a fully occupied average sized private car may compete with public transport services at certain off-peak times. However, despite its greater capacity, a full SUV has a higher emission factor per passenger kilometre. The impacts of human activity are more complicated than is often acknowledged. Including additional factors into analyses may provide counter intuitive findings. The overall impact of cycling is dependent on many factors such as diet, passenger fitness, speed and frequency of use.

  11. The link are ‘merely’ Euro5 compliant buses rather than hybrids – only the City Circuits are hybrid AFAIK.

    “The LINK Bus fleet comprises 20 new technology buses, which hit the streets of Auckland in September 2007.

    These buses were the first in New Zealand to meet the European Union emission standard, Euro 5, and have exhaust emissions that are up to 90 per cent lower than the old LINK buses:

    unburnt fuel is reduced by 58 per cent
    carbon monoxide is reduced by 67 per cent
    nitrogen oxides are reduced by 56 per cent
    particulate matter is reduced by 94 per cent.”

  12. Wendell as usual forgets about a few obvious issues. If PT is good enough that people are able to have real freedom of choice, and choose not to have a car, there is a huge environmental benefit for several reasons. If someone does not have a car they will structure there trips differently so they will complete more errands in one trip, and not need to travel so much distance overall. Another good reason for TOD, which will make this easier to achieve.
    Another benefit of not owning a car is one less car has to be produced. Each car that is built uses a tremendous amount of energy and CO2, so this is avoided.

  13. Yes Luke those are excellent points. One of my favourite transport books ever, Asphalt Nation, calculates that about 40% of a car’s environmental damage is caused in its creation. For someone to truly have the freedom to not own a car I think, as you mention, we have to seriously redesign the way we build cities, with TODs being an excellent start.

  14. The Link is definitely a diesel bus, just with high emission standards, the CC buses are hybrids…

    Some forms of PT have poorer environmental performance (on papaer) for example, ferries in America use twice the fuel per person, their advantage comes from the fact they usually only need to move the passenger less than half the distance they would otherwise travel by car…

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