Of smug and smog

So here in Boston we have moved from a two car commuting family to a single car that is used for incidental activities rather than regular travel. The kids walk to school while I walk and catch the bus to work. Even though it is the dead of winter I have actually sustained this new routine mostly due to the ability to work on the bus with my iPhone. The exercise is doing me good and at some level I am supposed to think I am contributing to the environment.

I also listen to podcasts on the bus as I did when I drove to work. So it was of some surprise that I listened to a recent episode of Tim Harford’s More or Less (while on the bus) about the environmental impact of bus as opposed to car travel. Tim repeats the issue in his FT column today.

According to my colleagues on the BBC’s More or Less programme, cars emit 127g of CO2 per passenger per kilometre and buses 106g, based on average occupancy. Even London buses average a mere 13 passengers.

Add my additional walking to the equation and my emissions may well be higher as a result of this change in activity. Indeed, as I like to work on the bus, I prefer to avoid the crowds. So on the bus I catch at 6:30am there are rarely the average number of passengers.

So what is the environmentalist’s response? It is that the bus “would be running anyway.” The idea is that buses have a regular schedule and so there are going to be times where they are more empty than full and other times where the reverse is out. So the appropriate thing is to look at the marginal rather than the average to work out net impact. As the bus is running anyway but a car would not, buses win.

Tim Harford points out, of course, that the same is true for air travel. Air travel is, for the most part, public transport. So the same argument applies to it: “the plane would be going anyway.”

An admittedly unscientific poll of environmentalists at dinner parties suggests to me that they think “the plane is making the journey anyway” excuse is unacceptable but “the bus is making the journey anyway” excuse is spot on – and that they have no coherent justification for the distinction. Their favourite excuse is “you have to set an example” – but surely, before you decide to set an example, you need to be sure that you aren’t setting a bad one.

The resolution lies in a very tortured argument.

For all you environmentalists out there, then, here is the justification for the double-standard of taking the bus but not the plane: it is that bus schedules might be insensitive to passenger demand, while planes are highly sensitive – and ever more so since the budget airlines arrived on the scene. Your best argument for taking the bus is a perverse one: that, no matter how many people do likewise, it’s the rare public transport tsar that will lay on extra buses.

The idea is that airlines and bus authorities put on buses to match demand. But airlines are in a competitive market environment while buses are managed by public authorities who are really bad at putting on extra buses. I’m not sure what the empirical evidence really is for that potential out but it strikes me that it could also go the other way. Public authorities have trouble cutting the 6:30am bus that a private company would happily do away with. In some countries, buses don’t leave until they are full — that is the market system at work.

This all suggests that just like we have ‘time of day’ airline pricing we need ‘time of day’ bus pricing. I should pay for travelling on my average emitting bus more than I would pay for stuffing myself into a crowded one. The interesting question is whether I would end up contributing to emissions less once all of this is in place. For the moment, there is no reason for me to be smug but I do enjoy being able to work while commuting.

12 thoughts on “Of smug and smog”

  1. Isn’t the bus empty also a condition of the efficiency and state of the public transport system in which it runs?

    For my time working in Europe I took rail/bus services where in less than ten minutes of alighting from a train the bus I needed was at the station. These bus services were all well patronised no matter what the time of day.

    So part of the problem isn’t the pollution inefficiency of a bus because it runs a regular schedule with services sparsely patronised, but that it doesn’t get people out of their cars and onto the bus for those services.

    Then there is the increasing use of gas and ethanol powered buses. Was the comparison made between them and the car or between diesel powered buses and the car?


  2. More people will travel by bus because of the iPad, Josh. Some of them to watch that movie or podcast, and read that book. Some will be on the look-out for easy pickings, since a lost or stolen iPad will be small enough to stuff down baggy pants.
    Keep it up, since it’s all about commuting. I can’t think of anything worse than a future where we depend on food we have to grow ourselves.
    Dave Birch http://digitaldebateblogs.typepad.com/digital_money/2010/02/vote-for-zits.html wrote about the tools of commerce, Ag and Au in the 1600s, Information now.


  3. A few points …
    1. Your emissions from walking are negligible vs your resting metabolism. You weigh a lot less than a car, and, unless you’re eating fossil fuels, your emissions are matched by CO2 absorbed by plants.
    2. Per-capita emission calculations should be based on full capacity, not average capacity. Carriers will only add new buses/planes when their existing vehicles are full.

    3. One trick the airlines use is to run a mixed fleet and match aircraft size to demand. Maybe the bus company could run smaller buses at 6:30am.


  4. There is also a question of how much extra fuel consumption is generated by your extra weight as a passenger (and luggage). My guess would be that it makes more difference in a plane.


  5. Joshua,
    You (and Tim Harford) need to distinguish between peak and off-peak bus services.  At peak, if full buses cannot cope with incremental demand, more buses will surely be laid on.  So, there is a marginal cost, but it is based on a full – not near empty – bus.  It also includes the capital costs of the bus.
    Off-peak, buses may be provided as a public service.  However, they may equally be provided because they are profitable.  Just as pubs and restaurants remain open mid-week, despite being almost empty, running near-empty buses off-peak can make business sense if variable costs are relatively low.
    Off-peak buses will be scheduled so long as patronage exceeds a threshold level.  Above this threshold, there is no marginal cost for additional passengers.  Below this threshold, there is no bus service.  Possibly, if you travel on a near empty bus,  you are keeping that service just viable.  In that case, you have a lot of pollution to answer for.
    Time-of-day pricing makes sense, but you have it back to front.  Peak prices should be higher than off-peak prices, because they must cover capital costs.  This is essentially how airlines price (but in a more sophisticated way).  Such pricing would lead to higher capacity utilisation and so lower average emissions, as well as a more profitable bus service.


    Joshua I can explain why those on the left love buses but hate planes.
    Buses are for poor people who don’t have any other option (“Anybody seen in a bus over the age of 30 has been a failure in life” not actually said by Maggie Thatcher but it could have been) .  Plane travel is a middle class western extravagance or for business (which is evil).


  7. A couple of small points:
    (1) A little-discussed but (in my case anyway) much lamented side of buses is noise pollution, especially if you live near a depot (as I somehow managed to do in three separate houses in Sydney.) Buses are much much noisier than cars and those night buses are particularly jarring. It’s MUCH worse than living under a flight path.
    (2) Emissions and energy use (and noise?) will vary a lot amongst buses, depending on the fuel they use, etc, surely?
    Worth noting that trams lack most of these downsides (though, of course, they’re less flexible.)


  8. This article, and Tim’s, is particularly interesting and insightful.  The best I have read on this blog in sometime… However,  it would be much improved by sticking you neck out and saying what you think we should do about this.


  9. It doesn’t really matter what the marginal change in emissions between walking, driving and the bus.  The main reason the bus may not be an effective way to reduce GHG emissions is because it is cheaper, leaving you money to spend on other goods you could otherwise not afford.  It’s called the Rebound Effect.


  10. Cameron,
    that is an intriguing suggestion.  I had never heard of the rebound effect before, so you have enlightened me there.
    Of course, in a general equilibrium analysis, we should also include the amount by which the extra time that the Professor spends on his iPhone contributes to economic growth and so increased carbon emissions.  I  imagine that this would be substantial.


  11. What? Isn’t the point that if every commuter was in a bus, then the total emissions would be far lower than they are now?  I think your argument just reinvents the sorites paradox


  12. Dave – Good points on the use of time and contribution to future growth.  But of course,  that use of time might also contirbute to Joshua developing innovative ways to reduce emissions.  The net effect can never be known, nor estimated I would suggest.


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