Use of Electric buses to improve Environmental performance of
bus travel by Sagar Shah

Introduction

In recent years there is a ton of hype around electrification
of cars and which is right for a reason that they contribute a lot to
congestion and there is huge amount of emission of major pollutants which has
made the urban air quality a big concern.

But here’s a less considered fact: Personal vehicles are probably the most challenging to electrify cost-effectively as they just traverse at maximum 4 people over a small distance in a 2-ton vehicle which consumes a lot of energy. The case for electrification or introduction of an alternate fuel is strong for other vehicles & Public Urban Buses top the list.

In this paper I will be exploring the implementation of electric buses to improve the environmental performance of Urban bus travel as well I will discuss various considerable points such as cost effectiveness of the electric bus as well as legislations, modifications in the regulations concerning the application of electric bus to the various markets of the world. The paper deals with Battery electric buses which will be referred to as BEBs for the rest of paper.

Why Battery electric buses?

Buses are the most important mode of transport all over the
world when public transport is considered. Buses for long have been used as a
main mode of transport for medium to short distance travel and have been the
most effective as they go through various routes. In March 2017, there were an
estimated 4.93 billion bus passenger journeys in Great Britain which is around
60% of all public transport journeys (DfT, n.d.)[1].

When talking about greener transport public bus transport are one of the worst contributors to two main contributors to air pollution namely CO₂ and NO₂. The emission of oxides is a result of fossil fuels used to run the conventional buses. Most of the conventional buses run of diesel.

It is found that public transport buses use 40,000 litres a
year which is 100 times more than a normal car. They run for 16-18 hr
continuously as compared to a car which has a usual use of 2 hrs. For this
reason, it is important buses are electrified as soon as possible.

Past development and Current scenario

For the last two decades there has been large developments in
making the electric vehicles a reality. It’s a tough task to design a bus which
can continuously work for 16-18 hrs and carrying passengers as much as the conventional
bus does. It is a known fact that all over the globe initiatives have been
undertaken to introduce electric buses.

The first uses of were mostly small, mini or midi-buses. The
improvements of battery technology from around 2010 led to the emergence of the
battery bus, including heavier units such as twelve-meter standard buses &
articulated wagons. Let’s have a look at the history of battery electric bus
developments throughout the years.

• In 2009, Shanghai catenary bus lines began to use battery buses.
• In September 2010, BYD Auto began manufacturing BYD K9.
• In 2013, battery buses introduced in Netherlands.
• In Germany in 2013 battery buses undergoing tests in Bremen and Bonn.
• The largest bus fleet in Dallan, China included 600 BYD buses.
• In 2015 BYD launch the first double decker battery buses.
• Botosani, Romania planned for public transport to operate fully electrically at a conversion cost of 20 million Euros

• In October 2015, the double decker buses were converted to BYD electrics
  with a range of 250km. London’s centre city access toll waived off for battery
  buses[2] (Wikipedia,
  2017).

It has been some very successful past
years for developers and there is a huge move towards electric bus seen all
around the globe. The quality of urban air is deteriorating and with cities
growing and urbanisation on the peak it becomes very important to have a clean
fleet of buses which can be cost effective and non- polluting at the same time.

Transportation Policies

London the capital city of the
England has for long been the economic hub and has been an example for the
world in terms of providing good public transport. The city is very well known
for its one of the best public bus services provided to its citizen. In the
past few years the air quality levels have been one of the most significant
worries for the policy makers. A study by Kings College shows that there are
almost 9500 people who die because of the air pollution. The NO_x and
the PM_(2.5) have been the biggest contributors to the air pollution
and they are highly emitted by the burning of fossil fuels by vehicles. CO_x
is the biggest contributor to greenhouse effects and they are the largest heat
absorbents and have caused a heavy increase in the global temperatures with
more and more emission of GHGs. With all these in mind considering the London
bus network there has been drastic steps taken to curb down the emissions and
go forward towards Zero Emission. Because of which following policies are
undertaken

• The
  Mayor of London announced a new £86.1m programme to cut harmful emission from
  London’s existing bus fleet.
• Around
  5000 buses more than half set to be upgrading to meet the Ultra-Low Euro VI
  Emissions standards, cutting pollution by up to 95%.
• The
  Mayor has also set out in his draft Transport strategy that by 2037 at the
  latest, all 9200 buses across London will be zero emission.
• The
  electric routes are part of major transformation the Mayor has asked TfL to
  deliver to reduce emissions from London’s bus fleet.
• One
  other important policy to clean up the Capital’s bus fleet include the phasing
  out of diesel only buses& a commitment to purchase only hybrid or zero
  emission double decker buses from 2018.
• The
  introduction of 12 new low emission bus zones, operational by 2020, this will
  see NO_x emissions along routes fall by more than 80%.
• In
  March 2017 TfL has introduced the first of 12 low emission zones, where only
  buses meeting the toughest standards are permitted to run.
• Using
  more Electric buses can dissolve the problem of greener transport &
  congestion.

To take a view of what the polices are doing on ground and
what people think about the current air quality situation in the city a poll
was conducted & designed by YouGov for a sample of 1000 Londoners. (YouGov, 2017). The results of the poll are discussed here:

88% think air pollution is a big problem, with 66% citing air
quality as bad and 72% wanted more stringent actions to curb air pollutions.[3]
This shows that even after the polices being so hard people are still concerned
more about the quality of air they breathe in when on streets of London.

As from all of this it is quite evident that the best bus
network in the world has outlined large number of policies & taken giant
strides towards making buses run by electric batteries. A lot of potential is
seen in the much anticipated zero emission buses to take over and make the city
a place to breathe freely in near future.

Key benefits of Battery electric Buses(BEB’s):

Electric battery buses bring with them lots of benefits. Most
important of them are the environmental benefits which will be talked more
about later in this paper. Following can be listed down as the major benefits:

Air quality improvement

 This will happen
largely because of the zero tailpipe emissions from the BEB’s. The levels of CO_x
and NO_x in the air are quite worrying in certain cities which is
predominantly around the city centre. BEB’s work on the principle of zero tail
pipe emission this should create a better ambient air quality for citizens.

Noise Pollution reduction

 Electric buses are
very quiet in operation and can be a big advantage in urban areas to reduce
noise pollution when compared to highly noisy diesel engine buses. If we
consider a peak hour rush in a urban street with lots of vehicles, electric
buses would contribute zero to noise levels as they can be near to perfect
quite when in operation.

Journey Comfort

 Electric buses have
been told to be very comfortable while on the move with passengers as it
reduces the jerks due to braking as it uses regenerative braking. The buses
have a lot more space when compared to diesel bus as they don’t have to be
equipped with heavy engines and other mechanical parts. The buses are much
lower to the ground and can also be a aid to disable people as it is very easy
to get on and off the bus

Maintenance cost Savings

 Due to very low
mechanical instruments needed for the propagation the wear and tear is heavily
reduced which can save a lot of money over the lifetime of the bus when
compared to conventional diesel buses.

Drawbacks

Range

For a large period, there has been a great enthusiasm towards
making public buses run on battery electric buses, but the hindrance is that
buses need to run 16-18 hrs continuously & there need to be enough power in
them to run all day long, but the range of the buses is limited &0 can only
run on smaller routes & not many double decker buses are operational till
date. Most of the buses are charged overnight and take almost 3-5 hrs to charge
fully and run for the whole day.

Heavy weight

To power a large vehicle like the bus there needs to be a
large battery pack inside the bus. The most famous BYD auto designed K9 with a
huge 345 kwh battery. The energy density is just near 100wh/Kg which means the
battery pack itself will be 3.5 tons. (Independent, 2016)

High initial costs

The cost of Conventional diesel buses is almost the half of
the BEB’s. This factor for a big span of time made BEB’s not feasible. But with
high research and development and a great downfall in the price of the batteries
for buses has somewhat narrowed the gap between the ownership costs of the
BEB’s and Conventional diesel buses. In future with more and more investment in
the research we can expect to see more drop in the price for electric buses and
it can be said that they will be more affordable by more markets.

Battery replacement costs

Batteries are the most important component of the BEB’s. Cost
of the replacement of batteries can be a very daunting factor when economic
viability is considered for the electric buses. As the costs of battery pack
are very high and the size needed for the bus is a huge one so can almost
result in somewhere around £20k after a span of 6-7year depending on the
manufacturers. But recently many companies have claimed to make this cost
diminished as the give a 12-year warranty of battery packs included in the bus
and which can be considered as the average life span of a bus.

Infrastructure Re-Development

A shift from one technology to another can prove to be a very
hard process. Electric buses would need charging docks for the buses to charge
overnight. This will need significant amount of money and it will add up to the
city’s electric demand.

Research in Battery

Success or failure of zero emission buses largely depend on
the success of the batteries used for electric buses. The reports on the highly
hyped London electric double decker bus which is manufactured by the ALD &
BYD as a joint venture which has the technological input form BYD, which is
world’s pioneer in BEB’s. (TFl, 2017) This BEB’s uses as
345kwh battery pack. BYD for long has specialised in a type of Lithium battery
called Lithium Iron Phosphate
(LiFePO₄). It is reported to have an energy density of just around
100wh/Kg. So, this battery pack will weigh a tremendous 3.5 tons before any
packaging, interconnects, cabling or BMS are considered so a weight of 4 tons
is more likely. The other drawback of LFP type batteries is its abilities to
take & release charge.

Now, to make the battery much more light and efficient
developments can be made in the direction of changing the materials used in the
batteries. For example, Tesla using lithium Nickel Cobalt Aluminium(NCA) the
P90D model S has a 90 Kwh battery pack which has an energy density of 140wh/kg.
Definitely this was for a car, but such developments must be made, and a lot
can be achieved in the electric drive technology of the electric buses.

Economically Feasible????

The idea of battery electric bus is viable or nor largely
depends on its economic feasibility. Any new technology at its advent is
expensive & is not affordable by all. For example, when smartphones started
to roll out they were priced highly when compared to the conventional mobile
phones. But with heavy investment in research & development & also
large competition around the globe to consumer markets the prices have come
down & the market has reached to a new pinnacle every year.

Battery electric buses can also be
considered more as an electronic entity rather than an automobile with more and
more research & the urge to go green on immediate basis will see a large
variation in the current buses & the buses to roll out in next 10 years.

As shown is the figure it is quite evident that due to heavy
turnaround towards electric vehicles there has been a drop of 80% in the price
of the main component of BEB’s battery packs. Prices have dropped yet the
initial cost is very high to own a battery electric bus having a range of 250
miles. With the change in technology there will be a need to improve the
infrastructure. This can add to the overall cost in bringing more BEB’s to the
roads pertaining the charging technology adopted, and the nature of change
needed.

Going forward it becomes necessary to study the feasibility
of BEB’s to make the electric buses accepted very firmly.

Transportation economy vary quite too much in every part of the world largely because of the different application of bus transport in every urban city.

Table1 shows the cost benefit analysis which compares the
Diesel Conventional Buses V/s Hybrid diesel buses and BEB’s.

The data has been collected from TfL statistics for bus and
other articles related to bus transport in London. There is a fleet of 9549
buses in London[4] (TFl, 2017) which comprises of
all the three variants included in the analysis. The assumption here made is
use of entire fleet as each type. From TfL report on Bus performance 16/17 it
is found that on average bus travels 35600 miles a year. This data has been
made a standard and remains the same for each variant throughout the analysis.
The BEB considered here is the BYD double decker bus currently deployed on the
route 98. The bus packs a 100Kwh/hr battery pack which uses slow charging to
charge overnights at the Willesden bus depot and takes about 3-4 hrs to charge
fully.[5] (Metroline,
n.d.)

The main aim was to find out the Overall operating cost of all the
vehicles and compare them.

As shown in the table the cost for the off-peak charging has been
assumed as 0.10p/kw, this charge can vary according to various boroughs and
different factors. On average bus travels 100 miles per day and price for
operation on each day is calculated as £4/day so which breaks down to 0.4p /mile.

Now we also know that the BEB’s usually have replacement battery due
every 6-7 years. But for this case the Buses provided by BYD has a warranty of
12years which is almost the lifetime for a bus. So, no maintenance cost is
considered in the analysis of costs for BEB’s. For BEB’s it can be considered
that there will be a need for new infrastructure development which may cause a
rise in the overall cost for the BEB’s. As we don’t have any figure for the
development of charging docks it is also not considered for the analysis. The
charging dock once developed can be used by many buses at the same time and
would last for several years without any maintenance need.

Following are the outcomes of the analysis:

• Ownership cost is almost double for BEB’s when
  compared to Conventional diesel buses but when compared to hybrid diesel
  vehicle there is a very skew difference in their ownership costs. This is
  largely attributed to high price rate of battery packs used in BEB.
• Operating costs of the vehicles show large
  variations as the cost for electricity is much low as compared to the cost of
  diesel. A single BEB can save up to approx. £42,000 which is almost the annual
  operating cost of a diesel hybrid bus. This means if the whole fleet is
  converted to BEB there can be tremendous savings on operational cost of public
  transport buses. Diesel and hybrid diesel buses also show a considerable
  difference but nowhere near BEB.
• Maintenance cost as shown in the table for BEBs
  are almost negligible as due to absence of mechanical spare parts the wear and
  tear would not happen. When talking about maintenance battery replacement cost
  if any should be considered but in the considered case it is zero as the
  manufacturer has provide a warranty of 12 years for the battery pack provide in
  the double decker bus.
•  Total
  cost per annum is the addition of ownership cost + operational costs which in
  the initial years is high for the BEB. This due to large investment needed at
  the time of procurement.
• The fig 5 shows the overall cost of operation
  over 12 years of life time, which shows that BEBs are highly efficient over the
  long term. Even if the battery is to be changed it could be adjusted in the
  same budget as for the hybrid diesel buses. The graph clearly suggest that it
  is extremely efficient to use BEB and can save around 350k over a life time
  when compared to a conventional diesel or hybrid diesel bus. For a whole fleet
  to be changed is somewhat hypothetical in near future but in his vision for
  buses Mayor of London suggested to only uses BEB by latest 2037. This means
  there can be billions in savings overtime if the project is successfully
  completed.
• Apart from this the most important benefit would
  be Zero-tailpipe emission from BEBs which can effectively and immediately
  improve the urban air quality and in turn save millions of pounds spent on
  health care and other projects to eliminate the effect of greenhouse gases.
  More about this will be discussed in Environmental impacts of BEB’s.

Thus, it can be said that currently the BEB’s are more
profitable if they provide the needed range of usage and the cost benefit
analysis proves and supports the implementation of electric battery buses
immediately.

Legislation and Regulations

With advent of new technologies arrives the need to amend the
legislations already present or design new legislations and regulations. It is
very important that legislations for BEB’s are shaped at every level of
governance and implemented. Following are the policies that can be made at
different levels to incorporate and encourage the use of battery electric
batteries.

International Organisations

Greenhouse effect is a global problem and pollution caused
anywhere would affect people everywhere, this should be kept in mind by each
organisation. Emission of GHGs is a serious problem in big cities of every
countries. Now to reduce it most of the countries in UN should stay committed
to save our planet earth from getting destroyed and there should be steps which
are mandatory for any member in a big organisation such as UN or EU. Any
violations must be severely dealt with and provisions of sanctions or penalties
must be made, this is because air pollution is not only causing deaths to
humans who breathe toxic pollutants, but it also is posing a severe threat if
the situations like now persists. Following are some important measures or
directives which global organisation must lay out:

Maximum permissible emission levels must be set out for each
country and no discriminations should be made between developing and a
developed country. China accounts for 23% of global greenhouse emissions[6] (Worldatlas,
2015)
all over the world.

Paris agreement COP 21 was signed by most of the world’s biggest
countries. US opted out of it as they would not be able to meet the levels set
which should not be the case. Bigger economies must stand as an example and cut
down of GHGs. More and more deals must be made out on global level and the
progress on it must be reviewed time by time to ensure its successful
implementation.

National level

Once the global agendas are set the countries on a national level
should segregate different policies for different sectors which can be used by
regulatory bodies and other industries and institutions to comply with the
goals set to meet the global agendas.

For BEB’s England has been very proactive in the Europe and
recently became the world’s first to use a double decker BEB. China on the
other hand has the largest market for BEB’s and has successfully managed to
incorporate them in public transport in various cities. These countries
policies can be set as an example for other countries. Following legislations
can be drawn from their policies:

• London has decided to only procure Hybrid
  buses or zero emission from 2018 and to only have zero emission buses by 2037. (TFl, 2017)
• Application of Ultra low Emission Zone(ULEZ)
  is done with dense traffic and higher Volume of CO_x and particulate
  matter in the air PM_(2.5). (TFl, 2017)
• Buses that comply to the most stringent norms
  of Euro VI are only allowed on the streets. (TFl, 2017)
• For china the have provided bus manufactures
  with attractive subsidies which has in turn made them the pioneer in these
  industries.
• Infrastructure development for BEB’s must be
  supported by government programmes.
• Efforts must be made, and more funds should be
  allocated for research in the technology of BEB’s. New ideas such as Solar
  charging docks which makes use of renewable energy sources must be encouraged
  so that BEB’s leave minimum carbon footprint.

Industrial

It is important that the manufacturers keep in mind the
emission levels and design the vehicles as per the norms.

More Bus operators should try and incorporate BEB’s and
fulfil their social responsibility.

Consumer perception

BEB’s have zero tailpipe emissions so they would not be
throwing black smoke right into urbanites faces. Diesel smoke is a big
contributor to 6.5 million deaths a year due to air pollution. This should
notably mean that use of BEB’s virtually means no emission of greenhouse gases
or air pollutants. The electricity from power plants generated may still emit
those pollutants, but even if it is powered by coal plants, a BEB would average
far less pollution per-mile than a diesel bus.

Electric buses are much, much nicer experience- lower to the
ground, much more space (diesel engines take a lot of space), no diesel burning
smell & no noise.

If the battery costs are brought down & with already low
operational costs the total cost of running a bus can be brought to half that
of a diesel bus. These advantages when passed to community would mean less
money to travel on bus.

BEBs can have positive social impacts as far as its
application is considered in urban areas. Air pollution and noise pollution in
urban areas have been associated in a lot of studies across the globe. BEBs can
also end up reducing stress levels.

Environmental Impacts

Air quality

As we know currently most of the fleet of buses run on
conventional diesel ICE engine. ICE engine is most popular but by burning
fossil fuels this are the several side effects of diesel buses. Apart from this
use of fossil fuels is at a peak & its price are also increasing day by day
with increase in demand.

 The figure shows that we will shortly be running out of fossil fuels.

The use of vehicles is increasing every year around the
globe and the demand is set to overcast the supply within next few years. BEBs
will help ensure we have an alternative to run our buses.

Air quality around the world has been in a grave condition
for the past few years. BEBs are technology which will help us provide freedom
from the emission which is caused by burning of fossil fuels. Diesel
conventional buses use up to 100 times more diesel annually when compared to a
diesel car. Currently the situation is so bad that a reputed daily guardian
published an article which headlined- ‘Revealed- Every Londoner breathing
dangerous level of toxic air particle.’ (Taylor, 2017) The article
highlighted the seriousness of air quality problem that we are facing. The
article stated that almost 95% of the capital’s population live in the rea that
are exposed to high level of particulate matter in the air. [7]

As the chart suggest the annual levels of PM2.5 are severely
high in and around the city of London. The situation is much worse when we the
levels are examined for central London. It is almost double the acceptable
limits suggested by WHO. BEBs when come into action will run through the
streets of the London but with zero tailpipe emission it is certain that this
level will drop certainly and suddenly. This particulate matter can be
described as something as toxic a drop of tar which will go down directly to
the lungs and then to bloodstreams. This very fine particulate matter can be a
reason for strokes and heart attacks. (Taylor, 2017)

The other major pollutant is Nitrogen oxides which is also
produced in our ambience, a pollutant which inflames the lungs, stunting their
growth & increasing the risk of respiratory diseases like asthma & lung
cancer. London has one of the most acute problem across the world.[8]

The figure shows how worse is the condition about nitrogen
dioxide in central London. It was reported that Putney High street managed to
break its annual emission limits in just eight days in 2016. The areas of
Knightsbridge, Oxford street, Earl’s court & Brixton following the suit
before the end of the first month. Government estimates 23000 people to die
pre-maturely from nitrogen oxide pollution. (Taylor, 2017)

Policies

Several policies are designed to maximize the use of BEBs in
London. Some policies have had a great impact in reducing the pollution from
the city while some have not shown any effects.

One such policy was to declare Ultra low emission zones in
the city where the vehicles meeting the highest standards are only allowed to
enter. But if we consider the scale of the policy it only secures about 300,000
citizens while ignoring the overall of 3 million which are affected by the
atrocities of air pollution.

The auto industry has for long tried and developed the
vehicles which emit lowest NO_x but have always failed. They have by
lobbying tried to have their bread and butter secure by keeping on doing the
wrong things to the environment. The norms have been manipulated and it is best
said that power is in money. The recently published EU limits have been an
example of this, Netherlands being the only country to oppose the limits. The
limits are set such that it allows manufactures could design for up to double
the acceptable limits by the WHO.[9]
(nelson, 2015)The powerful should understand that the
need is not to run from the problem but face it head on and take bolder steps.
Technology of BEB must be accepted by European manufactures. 60 years ago,
there was a ban on coal a similar ban is needed for diesel at least for urban
vehicles and specially for public transport.

Dark side

The BEBs run on electric and are zero-tailpipe emitting
vehicles but are they greenest option available for transport in urban areas?
Answer can be maybe no as the electricity used to charge the batteries of BEBs
come from the burning of coal ion a thermal power plant. It can be made the
greenest if options are found to make it run on renewable sources of energy.
Most of the electricity in UK comes from coal which is also a fuel which also
produces lots of carbon oxides and nitrogen oxides when combusted. Unless the
electricity coming to our grid is not by burning hydrocarbons there will be a
huge carbon footprint for any fully electric vehicle. But when a comparison is
to be done burning a fuel in industry would be much more efficient that burning
it on streets in different engines.

Other hazard can be of battery disposal after its use. BEBs
posses a large battery pack. Technology to recycle them must be developed so
that they don’t cause any hazard to environment. Most of the batteries are
thrown away & are used as landfill in various areas, these will eventually
degrade the soil & cause damage to vegetation also.

 It is important that
BEB should be developed in such a way that they should be 100% green and
environment friendly from well to wheel. This technology is developed as we
developed ICEs without assessing its impact on the environment. Cost might be a
barrier but compromising now could mean serious consequences.

BEBs can incorporate Other technologies

Buses in cities run over a fixed route and have a dedicated
lane in certain cities. A lot of research is put in developing an autonomous
car, the same technology can be used in buses with much lesser hindrance as it
would not have any other traffic on its way. Autonomous electric bus can take
out one of the largest cost that bus operators incur and that is labour cost.
This can make bus travel highly safe and cheaper in future with much more
accuracy to run on schedules.

Apart from autonomous drive use of renewable sources can be
done to produce electricity for the charging of BEB at the charging docks. Use
of solar energy to generate electricity and can be stored in storage cells and
then used to charge the batteries of the buses. This can cut down carbon
footprint to a very low level.  Such
technologies could make BEBs much more efficient and prove to be a game changer
in the public transport sector.

Conclusion

The idea of BEB has a clear future. It can prove to be the
game-changer to save the depleting air qualities in the cities and provide a boost
towards achieving a greener environment by cutting down the wasted fuel in
congestion, providing more greener space & by removing the deadliest diesel
ICE in our cities.

Implementing BEBs can not only be economically providing a
country with savings of hundreds of thousands of pounds on each bus but also
serve good to its citizens health by saving them from life-threatening diseases
which could be rampant because of air pollution. There ought to be a lot of
challenges along the path of revolution, but such has been the case with all
technological revolutions, and they’ve been dealt with before and I am sure
BEBs in near future will take over the market as the first choice for public
transport buses all over the globe.

References

Anon., n.d. Bus travel statistics, London:
Department of transport.

Bloomberg, n.d. s.l.:
s.n.

Independent, 2016.
New double decker bus launch in london. march.

Metroline, n.d. First
Zero emission Double decker, London: s.n.

nelson, A., 2015. EU
caves in to auto industry pressure for weak emissions limits. Guardian.

Taylor, M., 2017.
Revealed: every Londoner breathing dangerous levels of toxic air particle. Guardian.

tfl.gov.uk/corporate/publications-and-reports/bus-fleet-data-and-audits,
n.d. Bus fleet data and audits, s.l.: s.n.

TFl, L., 2017. TfL
and the Mayor announce more fully electric buses, London: TfL.

Wikipedia, 2017. Battery
electric buses, s.l.: Wikipedia.

Worldatlas, 2015. Biggest
Contributors to Air pollution, s.l.: s.n.

YouGov, 2017. YouGov
Air quality survey Results, London: s.n.

[1]
Data from Department of transport for bus travel.

Source for history: Wikipedia Electric battery buses.

[3] https://files.datapress.com/london/dataset/gla-poll-results/2017-01-26T18:50:00/YouGov%20Poll%20Air%20Quality%20Feb%202017.pdf

[4] https://tfl.gov.uk/corporate/publications-and-reports/bus-fleet-data-and-audits

[5] https://www.metroline.co.uk/blog/progress/world%E2%80%99s-first-zero-emission-electric-double-decker

[6] https://www.worldatlas.com/articles/biggest-contributors-to-global-warming-in-the-world.html

[7] https://www.theguardian.com/environment/2017/oct/04/revealed-every-londoner-breathing-dangerous-levels-of-toxic-air-particle

[8] https://www.theguardian.com/environment/2016/feb/05/the-truth-about-londons-air-pollution

[9] https://www.theguardian.com/environment/2015/oct/28/eu-emissions-limits-nox-car-manufacturers