Trolleybus Carbon Emissions

One of the most far-sighted elements of the appeal of trolleybuses is their claim to be the lowest carbon option for public transport. But is it really true?

The Canadian government’s environment agency, Environment Canada, compared several forms of road transport. Their report gives greenhouse gas emissions in grammes per kilometre*.

‘Clean’ Diesel Bus: 1966g/km
Diesel/Electric Hybrid: 1581-1725g/km
Trolleybus: 1930g/km

So there’s not much in it, and hybrids appear to be the lower-carbon option.

I must admit to not knowing how Canadian electricity’s carbon emissions compare to the UK’s, but they would have to be substantially worse to make trolleybuses lower carbon than hybrids.

And even attributing trolleybus electricity to the grid average is sleight of hand. Because they replace oil-fuelled buses that make no demands from the grid, trolleybuses add to overall electricity demand. This means more electricity will have to be generated somewhere. The only part of the grid with a large quantity of spare capacity are the coal power stations.

Whilst the averaged-out grid emissions are 480g/kWh, coal is 910g/kWh.

If we are to say that, as will largely the case, the power for trolleybuses will be extra coal generation then their carbon emissions would surely be far worse than the hybrid buses.

Also, the urgency climate change means we should not only choose low-carbon options but the ones we can deploy quickest. The vast infrastructure needed for trolleybuses mean they wouldn’t be on the streets of Leeds for at least six years. Hybrids could be on the road within months.

The trolleybus has the advantage of being ‘decarbonisation-ready’ because as the grid becomes powered by low-carbon sources, the emissions for the trolleybus go down. But as long as coal power stations are the standby that generate for extra demand, trolleybus emissions should be attributed to coal.

A low-carbon grid is a long way off. Hybrid buses – the mandatory design for all new London buses from 2012 – give the advantages of driving in urban areas on electric power so they have no localised emissions.

For the longer term, as renewable electricity supply hopefully becomes significant, electricity is clearly the low-carbon way to power our vehicles. Additionally, in one or two decades time oil prices are likely to be substantially higher than today, making the diesel and diesel-hybrids prohibitively expensive.

But why should we choose trolleybuses even then? At that far-off time, battery electric buses could take over. They have all the low carbon and zero-exhaust advantage, but with infinitely more flexibility. A trolleybus is shackled to its wires, only able to run for very short periods away from them. A battery bus can drive on any paved road. It requires none of the installation and maintenance work of the overhead wires.

Electric vehicles are fixed in the public mind as milk floats, but that is rapidly changing as modern electric vehicles take to the streets. Already we see Tesco and TNT using electric delivery lorries.

Trolleybuses have the advantage of ongoing supply, whereas batteries run out (Tesco cite the 100 mile limit as a reason to favour more hybrids over electric trucks). However there can be no more suitable project for battery vehicles than short-range, timetabled, centrally organised urban public transport.

In the long term we’ll get cheaper and more flexible public transport from battery powered buses at emissions comparable to a trolleybus. In the short term, until a renewables-based grid exists, electric vehicles cause more coal to be burned, making the diesel-hybrid the genuine low-carbon option.

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* Note: this post was first published with erroneous carbon emission figures. This has now been amended and relevant wording rewritten, but the first four follow-on comments refer to the original figures. We thank Irvine Bell for bringing the error to our attention.

10 comments to Trolleybus Carbon Emissions

  • Irvine Bell

    This site’s author(s) have got the facts wrong – the data quoted for ‘carbon emissions’ is actually for carbon monoxide emissions. If the author(s) had dug deeper into the reference site they would have found that trolleybuses running on UK grid mix have lower carbon emissions than all other practicable alternatives. And to argue that trolleybus electricity is incremental and must be calculated on the basis of pure coal fired generation is mendacious – exactly the same argument could be used for switching a light on. As a proportion of total grid generating capacity, electricity consumption by Leeds trolleybuses would be minute and the only fair comparison is on the basis of a grid mix average. That is unless a contract were entered into to purchase ‘carbon free’ electricity as at least one local authority has done by importing electricity – probably nuclear – from France.
    Over the longer term, the grid will / must / will have to get better – the other options can’t and won’t. And the grid author(s) miss the very important point that trolleys are zero emissions into the streets and don’t contribute to the severe air pollution problem from vehicle exhausts in British towns and cities – reference for example a recent Telegraph article at and a BBC news item at .

  • Irvine Bell

    Further to my earlier post, regarding hybrid buses being ‘standard’ for London from 2012 – that is very much an aspiration – hybrids are still very much on trial and my bet is that policy will change. Hybrid buses, after all are only (very expensive) diesel buses with regenerative transmissions that in practice have only marginal advantages over conventional (mechanical transmission) diesels. Outside London, no major bus group has any real enthusiasm for hybrids – First has just cancelled an order. If you look internationally you will see that decisions to buy hybrids have been essentially political and mostly only taken when subsidies from the public purse have been available. And the battery only range of hybrids is so limited – a few km – that driving any significant distance in urban areas in battery mode is just not feasible. Regarding pure battery vehicles, these have, in principal, similar environmental credentials to trolleybuses but in practice range is too limited. Even with the best of modern batteries available or envisaged, getting an acceptable range means having as much as something like 50% of gross weight as batteries – look at the figures for the Tesla Roadster. Actually having 50% of your gross weight as batteries may be practicable for a car, but it isn’t for a bus. Consider a typical 17 tonne gross bus (trolley, diesel or hybrid) with an unladen weight of around 11 tonnes and able to carry up to about 6 tonnes (say 90) passengers. That bus would need about 8 tonnes of batteries to get a reasonable – say 200 miles – range. But you can only get about 6 tonnes on the bus without exceeding the 17 tonne gross weight, so you put 6 tonnes on and tell the passengers to walk. And battery buses do require a significant charging infrastructure, especially if in service (rapid) recharging is contemplated The best use of batteries is to give trolleybuses a few km of off wire capability. In the long term we will NOT get cheaper and more flexible public transport from battery powered buses at emissions comparable to a trolleybus. There simply are no practicable, cost effective and as environmentally friendly alternatives to trolleybuses, except trams where traffic volumes can justify the very much higher investment required. And trolleys can be got on the streets quickly – in Salzburg it takes no more than a few months from decision to implementation. The reason NGT has such a long time scale is because there is a lot of civil engineering involved that has very little to do with whether the vehicles are trams, trolleys, hybrids or whatever and because UK decision making has (so far) proved to be very long winded.

  • I note that you quote TfL’s policy for hybrid buses as being something of merit.

    I also note that you are solely interested in global carbon emissions – even though whilst there is no doubt that the global climate is changing there is still doubt as to whether humankind or the little – reported other factors are causing these changes. Please investigate undersea volcanic action as being a significant source of carbon emissions. Also investigate the simultaneous changes underway elsewhere in our solar system – on Mars, Uranus and more.

    Maybe ‘solar variation’ is an issue here – perhaps with there being long term cycles which a civilisation barely a couple of thousand years old knows little about?

    In the meantime, some scientists are pondering whether the ‘warming’ aspect of climate change has ceased and if we could actually be heading towards a mini ice age. There is a precedent for this, as a mini ice age preceded by a warm period is within our recent historical reality.

    However, whilst the causes of global climate change are still only theoretical, there is no doubt that urban air pollution harms human health and even kills people. 50 years ago we (as a nation) faced such severe air pollution that Parliament passed new legislation which resulted in a significant improvement in air quality. Since then however there has been a very large increase in the number of oil burning vehicles on our roads and we are slip-sliding backwards… indeed the situation is now of such severity that many British urban areas are failing to meet British air quality laws, yet alone EU regulations. For its part our erm ‘wonderful’ government’s response is to seek derogations and ‘more time’. As if that is capable of solving anything!

    Did you know that the EU is now intending to sue the British Government for the poor quality of air in our towns and cities?

    According to a (British) Government report issued by the <> air pollution hastens the deaths of between 12000 and 24000 British people a year and is associated with 14000 and 24000 hospital admissions and re-admissions – causing sufferers and their families untold amounts of misery and costing our health service & taxpayers £billions.

    Yet what are you promoting?

    More diesel fuelled vehicles instead of direct grid powered electric buses – this being the direct opposite of what we urgently need!!! Hybrid buses still spew out PM10, NoX and other pollutants straight in to the air which we breathe. How many buses have waste gas pipes at about the same height as children sitting in pushchairs? These pollutants go deep into their lungs, potentially resulting in asthma and other respiratory illnesses. Of course everyone else also breathes in this polluted air too. Trolleybuses do not give off any tailpipe pollution at all.

    Your pro-diesel campaign suggests that the railways should be diesel too. So, by extension you are suggesting that the Bradford, Skipton, etc line which was only electrified about 15 years ago should be converted back to diesel.

    Using your logic, Sheffields’ trams should be diesel powered as well.

    Would it not be better to be campaigning that ALL of the buses in Leeds / West Yorkshire should be as clean and non-polluting as possible? Trolleybuses make this possible. They are as clean and city friendly as trams. Hybrids are only ‘less dirty’ than other types of diesel bus – with the added and barely ever talked about environmental and financial issues related to disposing of the spent batteries.

    I did not note in your equation the financial costs and quantities of noxious pollution emitted when the batteries are created and (later) disposed of. That is assuming that the spent batteries are recycled in an environmentally sound way!


  • Thanks for publishing my comment.

    Alas a few words seem to have gone astray – the (British) Government report which reveals the shocking toll of human illness and premature death that is directly attributed to air pollution was published by the “Committee on the Medical Effects of Air Pollutants” (COMEAP). More about them can be found here…


  • Merrick


    Responding to your first comment:

    You are absolutely right, I quoted the wrong figures. This is one of the great things about online writing, we can check claims, catch errors and revise things so issues become clearer.

    Thankyou for pointing that out, this has now been corrected and the Environment Canada figures have been used instead. These show similar emissions for trolleybuses to diesels. This may be because Canada has an especially high-carbon electricity supply. Can you find a figure for that?

    But still, the trolleybus site figures seem to say a conventional diesel bus emits a very high 3800-3950g/km. Where is this figure sourced from?

    You say that basing trolleybus emissions on coal is mendacious and ‘the same argument could be used for switching a light on’. We already power our lights from electricity; as such, they are part of present grid demand. To shift a significant element of our energy demand from oil to electricity means an increase in electricity demand; continuing with present demand for lights etc does not.

    Yes, the Leeds trolleybus demand will be small, but that’s hardly the point. We’re talking about decarbonising the transport system. If you argue the demand is small then you’re also saying the savings in carbon are small – your argument cuts both ways and thereby undoes itself.

    I’m not trying to pull a fast one here; on the contrary, I’m trying to get us to see electricity usage clearly. And I readily apply the same argument to other ‘low-carbon’ transport options like electric cars and, indeed, electric buses. these things are, as I said, ‘low-carbon ready’, but until the time when we have a largely renewable grid or coal stations are offline, they add to demand and that will be supplied by burning extra coal.

    With road transport, unlike trains, we have other options besides present oil fuelled models and pure electric – these are the ones I advocate. Principally hybrid buses as a changeover technology until we can have electric buses, and penalising car use to get people on to public transport. Even the filthiest idling rushour bus beats the 35 cars it replaces.

    And I didn’t ‘miss the very important point that trolleys are zero emissions into the streets’. I mentioned it twice, which for a 500 word piece about a different subject is quite a lot. It is indeed a major advantage of trolleybuses over diesel (as is the fact that oil prices in 20 years are likely to be astronomical, so we need to be moving towards oil-free transport as soon as possible); but it is equally true for electric buses.

  • Merrick


    Responding to your second post:

    Transport for London’s position on hybrids isn’t ‘very much an aspiration’, it’s a set policy to be enacted in three years. When the governing body of London’s transport has such a definite and short-term policy, to disprove it you’ll have to do better than saying you ‘bet’ it’s not true.

    You’re right that there’s not much demand for hybrids outside London. That’s because they’re expensive and so who would choose that if other cities will let them keep running their old diesels? It doesn’t discredit hybrids any more than trolleybuses are slighted by saying there’s not much enthusiasm for them outside Leeds.

    Your concerns about the range of electric buses were dealt with before you raised them. In the post I point out that ‘there can be no more suitable project for battery vehicles than short-range, timetabled, centrally organised urban’ vehicles. Rather than plugging in the bus and waiting a few hours, you have depots that swap empty batteries for full ones. (This is the model being used by Shai Agassi for electric cars, and is, I believe, the thing that will make them practicable. you fill up once in a while at a refuelling station, just like oil fuelled cars).

    Whilst Salzburg may have got trolleys on the road quickly, that – as you concede – won’t happen here. In emission terms, the reason why it won’t happen is irrelevant.

    So my point (that hybrids can be on the road in months whereas we won’t have trolleys for six years at least) is completely unaffected. As is the consequence of that, namely that we need lower carbon technologies deployed as quickly as possible.

    And just to reiterate, I’m not pulling a fast one; I thank you for you thoughtful comments and believe there is a debate to be had as none of us have all the right facts and arguments. I think the trolleys have numerous positive aspects, and I hope that’s clear. I also think hybrids have numerous problems.

    The real enemy is urban car use, which is far higher carbon, air-quality assaulting, dangerous and largely unnecessary. I hope the Alternatives section of this site covers that.

  • Merrick


    I do indeed regard TfL’s policy on hybrids as being of merit. And if you want to disabuse me or anyone reading this of that idea then you’ll have to give more than a sarcastic insinuation.

    Your points about climate change are a little off topic and somewhat novel. The greenhouse effect and carbon dioxide’s part in it are proven. Human activities have caused a net increase in atmospheric carbon dioxide. Put an extra few blankets on your bed at night and see if you get warmer. It’s really simple. Which is why over 99% of meteorogists and all the major bodies of scientists in the world concur. If you can supply any peer-reviewed science to the contrary, essentially turning elementary physics on its head, then I’m all ears. And I’d bet there’s a Nobel prize in it too.

    I completely agree about the importance of local air quality. However, climate change is the greatest threat facing humanity and we need to instate policies that respond accordingly. Fortunately, many of the responses to both problems are the same. Primarily, we need to drastically reduce urban car use. Hybrids emit lower amounts of exhaust emissions than standard diesel buses, and electric buses, like trolley buses, none at all.

    The truly low-carbon methods of urban transport – walking and cycling – aren’t helped by trolleybus. Its bendybus design is a menace to pedestrians and cyclists (as it is with the diesel bendybuses currently in service), and the outrageous fragmentation of cycle lanes – including the removal of some – is an attack on cycling.

    You’re right that I didn’t mention the financial cost of pollution from manufacturing batteries. Nor did I mention the equivalent costs of manufacturing trolleybus infrastructure. Unless you can compare them, you’re not really making a point. And your stuff about trains criticises me for something I didn’t say and don’t believe.

  • Irvine Bell

    Hi Merrick,

    Thank you for your email and thank you for noting my pointing out of the error(s) in the original data. The original data showed carbon monoxide emissions into the environment for different modes, which for any mode are minute compared with carbon dioxide emissions.

    I have had a look at the (amended) and your post which now reads

    “Trolleybus Carbon Emissions
    One of the most far-sighted elements of the appeal of trolleybuses is their claim to be the lowest carbon option for public transport. But is it really true?
    The Canadian government’s environment agency, Environment Canada, compared several forms of road transport. Their report gives greenhouse gas emissions in grammes per kilometre*.
    ‘Clean’ Diesel Bus: 1966g/km
    Diesel/Electric Hybrid: 1581-1725g/km
    Trolleybus: 1930g/km
    So there’s not much in it, and hybrids appear to be the lower-carbon option.
    I must admit to not knowing how Canadian electricity’s carbon emissions compare to the UK’s, but they would have to be substantially worse to make trolleybuses lower carbon than hybrids. ….”

    The link you give to the report at is already familiar to me. It is one of a set of reports and studies used, in a very partisan way in my view and the views of others who spent a lot of time analysing all the reports and studies to justify the recent abandonment of the Edmonton trolleybus system. You may care to note the caveat in the report “This report has not undergone detailed technical review by the Science and Technology Branch. The content does not necessarily reflect the views and policies of Environment Canada.” on page 7 of the PDF file.

    I would not however disagree with the figures in the report that show that CO2 emissions for hybrids might be 12% to 20% lower than conventional diesels – these are about what one might expect (and much less than the 40% or so figures often touted by hybrid proponents). However, the Edmonton electricity grid is coal based – more so than our own – and yet despite that, the trolley CO2 figure is still, even if only very slightly, better than conventional diesel. That could be a good argument for running trolleybuses on indigenous coal rather than running diesels on imported oil. Also, as I remember one of my chemistry teachers remarking over 40 years ago, oil (unlike coal) should be regarded as too valuable as a raw material to burn!

    However, if the same trolley was assessed on its home grid in Vancouver, where the grid is mostly hydroelectric, the carbon emissions would be near to nil.

    Based on the electricity consumption of the type of trolleybus used in the evaluation in Vancouver where the reported electricity consumption was 2.14 kWh per km, the carbon emissions for such a vehicle on the UK grid average would be about 2.14 times 480 (your figure) equals 1072 g/km – some 32% lower than even the best diesel/hybrid data that you quoted above and with the potential in the longer term to go towards zero in a way which can never happen with any oil fuelled vehicle (for example without having to turn land needed for food production over to bio fuels).

    May I suggest by the way that you obtain a copy of “Sustainable Energy – without the hot air” by Professor David Mackay and study the material in the book about better transport which comes down heavily in favour of public transport and electric vehicles (page 129)? The book can be downloaded for free from .

    As I noted earlier, I simply cannot accept that it is some kind of ‘sleight of hand’ to use grid average data for CO2 estimations. It is Machiavellian to do otherwise, unless trolleybus energy consumption was to be so large that it significantly distorted current patterns of electricity generation and consumption – which it won’t. The ‘incremental generation must be coal’ argument that you seek to deploy can be used about any ‘incremental’ load – such as you switching a kettle on. In fact if you read David Mackay’s book which goes into some detail in how an electricity grid is managed, you might see that incremental generation could be hydroelectric for example.

    Regarding your views on exchangeable batteries etc., for buses operating intensive urban networks, you really, with the greatest respect, I feel must have no appreciation of the practical realities of trying to operate such services in real life conditions or of the logistics of trying to make batteries work or the costs or the infrastructure requirement or of recharging issues. The last time I spent a lot of (email) time discussing the actual practicalities of trying to operate with batteries with a proponent of such an approach, he convinced himself that the best way to do it was to put up overhead wires over most of the routes so that batteries could be re-charged on the move! The (urban) battery bus will only be truly practicable, other than for niche applications, when we have a battery than as an energy store can match the weight, size, cost, safety, efficiency and convenience of refilling of a tank of oil fuel. That is a very long way off, if ever.

    As it happens, I think that there could be a significant place for battery cars in the nearer term future (you refer to ) but buses are very different animals to cars – I spent more than 25 years involved in their engineering and operation and like to believe that I know.

    Regarding TfL’s position on hybrids being the future standard, it is not so long since TfL though that hydrogen fuel cell buses were the future until experience convinced otherwise. I am quite happy to place a (modest) bet with you that TfL will not go seriously down the hybrid path! Shall we set a determining date in say 2015 when I expect that enthusiasm for hybrids, even within TfL will have run its course?

    I do quite agree with your point about urban car usage. While battery cars may alleviate air pollution problems, they won’t help with, for example traffic congestion. The future in our urban areas just has to be switching transportations from cars to public transport and other modes like walking or cycling. I must confess to being not comfortable cycling amongst other traffic, but I do as much walking as I can. As for buses at least, I have probably spent more miles driving them than riding them.

    Best wishes,

    Irvine Bell

  • Irvine Bell

    Sorry Merrick, I have noticed that I did not deal with your question

    “But still, the trolleybus site figures seem to say a conventional diesel bus emits a very high 3800-3950g/km. Where is this figure sourced from?”

    If you look at , you will read that the bar graph that I assume you have read data off has below it:

    “Approximate total greenhouse gas emissions based on New York City duty cycle (includes CO2, NOx, CH4, NMHC and CO) in g/km of CO2 equivalent
    Compiled by Kevin Brown (University of Alberta/Edmonton Transit System Advisory Board) using data sourced from: Northeast Advanced Vehicle Consortium, Edmonton Power, San Francisco Municipal Railway.”

    I guess that you are surprised by the greenhouse gas figure(s) for the diesel, which you read off as 3800-3950g/km is/are much higher than other figures that we have discussed in this column. There are a couple of factors that need to be considered in interpreting the data from this graph and these are:

    1. The figures are in CO2 equivalent but actually include all greenhouse gas emissions associated with the modes compared. For diesels for example, that will includes NOx emissions which have a greenhouse effect in addition to the CO2 emissions.

    2 Greenhouse gas emissions are duty cycle dependent. CO2 emissions bear a linear relationship to fuel consumption which can vary over a range of something like 2:1. This data is for a particular and obviously very demanding duty cycle. It is the comparisons that are important, not the actual values.

    If one compares a trolleybus with a diesel bus operating an urban duty cycle, the diesel is about 25% efficient fuel filler to wheels while a trolley is about 90% efficient wires to wheels. If diesel or similar fuel is used to generate electricity in a modern thermal power station, the conversion efficiency, fuel to electricity, is in the region of 55% or better (large diesels do about 55% and gas/steam turbine combined cycle as much as 60%). Losses in transmission (grid and overhead wires, etc) are around 20% so the overall efficiency of a trolley, ‘fuel filler to wheels’ is around 40%, implying on a strictly like for like basis that trolley CO2 emissions will be around 60% of those of diesel. Basically it is very much better, if one is going to burn a fossil fuel, to burn it in large fixed plant and transmit the power electrically to a vehicle, rather than burn it in a small mobile plant on a vehicle. But trolley vehicles, unlike internal combustion engined vehicle have the potential to use electricity from low or zero carbon sources. If Leeds wishes, the power for trolleys could be purchased from the outset from a low or zero carbon source or sources. Whatever merits or demerits NGT has as an overall scheme – trees lost here, cycle lanes lost there, faster and more reliable journey times for NGT vehicles compared with current buses, etc., – the trolleybus is currently by far and away the most environmentally friendly way now and in any reasonably foreseeable future to operate it. Electricity is the low greenhouse gas, sustainable way, to operate urban transport (whether road or rail) and has the very big advantage of zero emissions at the point of use. No internal combustion engined vehicle can seriously compete with the environmental advantages of the electric vehicle for urban transport. Whatever good or bad reasons that you have for seemingly trying to knock the NGT proposals, please do not knock them on account of the possibility of electric operation.

  • Tcheney

    The numbers for Edmonton include a lot of coal power in the Alberta grid . The rest of Canada primarily uses hydro and nuclear.

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