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London Plans Hybrid Bus Fleet

The Guardian. London’s Mayor Ken Livingstone wants every new bus from 2012 to be a hybrid that will generate 40% less carbon dioxide than their diesel-powered predecessors. The City will begin putting 500 hybrid buses in service each year.

Transport is a significant contributor to London’s carbon emissions, accounting for 20% of all CO2 generated in the capital. London’s 8,000 buses create about 5% of all the transport emissions.

“We take very seriously our role in cutting CO2 emissions and tackling climate change,” said Peter Hendy, London’s transport commissioner. “We are sending a clear message to London and the transport industry that we are serious about this.”

An entirely hybrid fleet would produce 200,000 fewer tonnes of carbon each year. London is aiming to reduce its carbon emissions by 20% by 2020, rising to 60% by 2050, levels that are in line with the government’s carbon targets.

According to The Guardian, Transport for London (TfL) expects its all-green fleet to include biofuel-powered buses as well as hybrid and hydrogen-propelled vehicles. It expects to subsidize the introduction of more hybrid buses next year, in partnership with one of the capital’s bus operators. However, it cannot accelerate the program because manufacturers do not mass-produce hybrid models due to lack of demand.

TfL hopes the 2012 targets, backed by taxpayer subsidy, will spur production of more fuel-efficient buses. The organization is also exploring ways of cutting emissions from cars and trucks, which account for three-quarters of the CO2 generated by transport in the capital.



Now, will they go Euro, American, or a combination of the two?


Didn't Seattle find that GM's hybrid buses really don't improve mileage?


It depends on the way you use the hybrid buses, and what type of hybrid powertrain you use. Currently, GM's hybrid bus powertrain achieves better fuel economy on city streets, where it can use regeneratve braking in stop and go diving patterns. Highway fuel mileage does not fare as well. London will likely use hybrid buses on city streets, and thus will probably see significant fuel savings.

Rafael Seidl

More on the trial TfL has already conducted on the diesel hybrids here:

Toxic emissions are way down compared to the old Euro III compliant ICE-only models, especially since the hybrids had DPFs as well. Noise levels were down 30%. Fuel consumption was down 40%, CO2 down 38% (why the difference?)

All in all, it clerly makes environmental sense to hybridize city buses (no data was given on TCO). This is true even if the total improvement in London's CO2 balance as result of this program is just a miniscule 20%*5%*500/8000*38% = 0.0024% in the first year.


Hi all, Considering the very long distance a bus travels in a year it probably also makes economic sense.
Hopefully in 2012 the batteries will be even more robust.. needing less maintenance and replacement.


Rafael Seidl,
"why the difference?"
It could be due to:
a)Calculation errors and rounding of numbers
b)motor oil consumption
c)cleaner diesels mean CO2 instead of particulates and CO.


Surely buses and other stop/start delivery vehicles are the first things to be hybridised.
Hybrid cars are really just a green trophy for most people - they do it because it makes them feel good - and sounds good at dinner parties.
Hybrid delivery trucks, on the other hand could take a decent chunk of CO2 out of the system.
Another idea I had is avoiding needless braking: regenerative brakes are 20 - 30% efficient at recovering energy, which is fairly crap. A better idea would be to reduce the maximum speed in town ( to the speed limit for instance) or starting engine braking as soon as it becomes obvious that you will need to brake - say as soon as a traffic light goes orange. The kinetic energy of a vehicle is proportional to the square of the speed, so reducing the speed by 10% reduces the energy by 21%.
That is 21% less energy to recover at 20% effeciency.

Thomas Pedersen

WOW, these buses seems like a major step forward in terms of reducing the negative impact of bus transport, including all the items mentioned on the page linked by Rafael.

Actually, we had hybrid buses driving around in my town about ten years ago. They operated on a SAAB 2.3i engine, at that time the cleanest ICE engine WW - supposedly cleaner than London air, btw. These buses were a major drag to ride, because they were immensely slow. 0-25mph took almost ten seconds :-( But even worse, they had en engine roaring all the time, which was quite annoying at the bus stop, not least because it is counter-intuitive. I'm pretty sure they had lead-acid batteries, which explains the sluggish acceleration.

I seriously hope these new buses are better, but I think the chances are quite good, given ten years of further development. Hopefully they have ultra-caps as an intermediate step, although they are not mentioned on the schematic. Come to think of it, they could probably do with all ultra-caps and no batteries for this kind of heavy stop'n'go rhythm. If I am not mistaken, ultra-caps are capable of vastly more charging cycles as well.

I think very few buses in London ever travel more than 200-300m between braking and accelerating, mostly due to heavy traffic, making hybrid drive a very promising option. The diesel engine on these buses is 1.9 litre, i.e. compact car size. The wheels are driven solely by a 120 kW electric motor, giving a top speed of 40-45 mph.

The hybrid drive unit is made by Enova Systems and has a torque of 650 Nm (480 ft-lbs). More details can be found here:

Rafael Seidl

Mahonj -

a typical delivery driver won't pay attention to fuel economy unless he/she can increase his/her take-home pay as a result. It would be great to see a forward-thinking delivery service company make part of its drivers' compensation package dependent on the fuel economy they achieve. The following page provides links to thrifty driving styles etc. - especially for hybrids:

In addition to changing driving habits, carmakers should bet on improving the recuperation efficiency of those vehicle classes that most depend on it. That means leveraging power-centric hybrid concepts based on ultracaps, hydraulic accumulators or air pressurization. All of these are capable of supporting rapid deep charge/discharge cycles with little or no wear and tear. They do not, however, support switching the ICE off altogether during slow cruising.


Do not get me wrong. 0.0024% decrease in CO2 emissions really does not worth the efforts from “global” perspectives. Especially when it is due to conversion to straight diesels (hybrids are totally different matter), which could not sustain further CO2 emission reduction. . But 40% reduction in fuel costs, and reduction in maintenance due to lower brake wear, and reduction in local air pollution is really a big deal. Worth even near-term monetary losses.

Harvey D.

The world needs 1000 more mayors like Ken Livingstone.


Harvey D,
Two of them are named (Mayor) Bloomberg and (Gov) Schwarzenegger.


What's wrong with the natural gas/electric approach that Denver uses on their pedestrian mall? This seems like a cleaner approach than using diesel. The other thing Denver did was form their own company because they couldn't get any firm to manufacture a bus to their specifications. Maybe London should consider this since apparently no one is willing to ramp up production in the short term.

Just asking. It may be that the Denver buses are considered too slow, but given all the stop and go driving in London, they may be adequate.

The Denver buses are an adjunct to Denver's 1.3 mile pedestrian mall. Perhaps that concept should be expanded to much of Denver and much of London, for that matter. Maybe transportation should be kind of like the use of meat in a Chinese meal -- more of an appetizer, but not the main course.

As Rafael rightly points out, better buses will have a minimal impact on carbon emissions. Where will the rest of the reductions come from? Even if you cut transport in half, you've still only reduced overall emissions by 10%. Green Building Congress, anyone?

Rafael Seidl

t -

Wrt green buildings: the German government is contemplating a new scheme under which all residential homeowners must obtain an "energy passport" prior to renting or selling the property. These document are to be produced - with typical Teutonic thoroughness - by an army of consultant engineers, based on actual utility bills and/or measurements of a given property's thermal performance (cold bridges, draughts etc.) Critics claim these consultants will be in league with construction companies angling for expensive insulation retrofit contracts. The warn that excessive insulation measures can suppress natural ventilation, promoting the buildup of humidity and mold in inaccessible places.,1518,445103,00.html

Wrt making a big dent in global warming: a recent study of gas flaring in oil-producing countries, based on satellite imagery, estimated that in 2004 nearly 200 BCM were wasted world-wide. For reference, total US consumption of natural gas in 2004 was 22.43 TCFT = 635 BCM. Natural gas accounts for roughly 1/4 of total energy consumption by the US.

In other words, flare gas reduction would easily be the single most effective conceivable climate change measure. Unfortunately, it requires the co-operation of many governments plus either a local market (e.g. a CNG vehicle fleet) or a global LNG/GTL infrastructure. The World Bank's GGFR initiative has a staff of 10 people - talk about priorities.


I wasn't suggesting that the drivers buy the trucks - the fleet owners would.
Drivign style - all the hybrid cars people say is pump your tires, don't speed and anticipate stops. Which is essentially what I am saying.
What I was trying to say is it is easier to save energy by not going too fast rather than by adding inefficient regenerative braking.
Am I right in saying that ultracaps can absorb more power than a battery, but less energy, and might be better for sudden braking ( at the cost of complexity )?
The bit on flaring gas is interesting - any comments on underground coal fires ? - Has anyone figured out a way of putting them out ?
[ for instance ]



Flaring of NG is only tip of the iceberg. A lot of methane is leaked in atmosphere during extraction, purification, transportation, and especially during local distribution. I had access to reports, estimating venting and leaking of methane in USSR between 10 and 15 % of all NG produced. Current numbers for major pipelines are lower, but leaks from run down local distribution systems in all countries of former USSR are higher. Situation in China, middle East, and India is probably even worse. Considering that methane is 20-30 times more powerful GHG agent then CO2, (concentration of CH4 in atmosphere increased 3 times from pre-industrial levels), low estimation is that GHG effect of NG leaks is bigger that from all transportational sector.

One could easily understand, where real reduction in GHG emission are. But it is not as sexy as bashing US gas guzzlers.

For quite simple article look at:!_

P.S. As you know, I do not give a hood about GW bogus. Just pity how precious resources are wasted. And I am talking not only about NG.


Definately stop the gas flaring...that is so wrong on many fronts. Cant believe thats not a proftable biz.
Ive seen diesel cantenary buses in Seattle...were those not hybrid?


The Seattle breda busses were 'hybrid' only in the sense that there was a diesel powertrain and an electric powertrain. They were sort of an awful design, and would have been far better if the diesel engine drove a generator rather than having all the extra weight of a completely seperate powertrain.

Not sure if the current diesel trollybuses are hybrids, but I dont think so.

Thomas Pedersen

Gas flaring is wrong on so many levels. Waste of valuable ressources is the worst, I think.

But emitting gas without burning it is worse!

I remember reading once, that NG engines normally leak around 5% of the fuel. That corresponds to a doubling of green house impact, since methane is roughly 20 times as powerful as CO2.

In Denmark we have a lot of small municipal CHP plants (2-5 MW power), mostly based on poorly adopted gas engines, based on diesel engine design (locomotive engines). Their purposes were three-fold; 1) utilize large indiginous NG ressources, 2) Get district heating to semi-rural areas, 3) reduce GHG emissions. The latter has certainly NOT been accomplished. And if you add the leakage of gas through the pipelines, it's even worse.

Even so, I think the London hybrid buses are still cool (back on topic)


You are right on all counts. Hybrid buses are cool. Flaring of NG is a shame. Leaking of NG is even worse.

Whatever concerns to NG engines. Classic four stroke diesel engine has intake/exhaust valves opening arranged to vent about 5% of fresh intake air into exhaust. This is made for two reasons: to assure perfect ventilation of combustion chamber and to cool down exhaust valves. In many cases when such engine is converted to run on NG, in order to save on valvetrain alteration, timing of intake/exhaust valves closure is retained the same. It really leads to venting off of about 5% of incoming charge of air/NG mix. However, modern NG engines, both stoichiometric (extremely low polluting), and lean-burn stationary diesel-generators have their valvetrain arranged to eliminate this vent-off. So this GHG emission and waste of fuel is eliminated.


If you use CNG for the ICE you also benefit from reduced tailpipe emissions, lower noise and reduced oil dependency.


Thats Ok but I think we are going to face a North American NG shortage even before oil shortages. Things don't look good for North American NG production. The rig counts are increasing rapidly but output isn't. Not a good sign especially when you have the blacl hole called tar sands which will consume all the NG we can produce in the future.


"Hybrid buses' fuel economy promises don't materialize"

vudya sagar pandey

sir please send me more information about this topic .

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