Transport and Climate Change
Chapter 2: Trends in UK transport emissions
Introduction
2.1 In order to establish the role of transport as part of wider efforts across the economy to
deliver the most cost-effective carbon reductions consistent with the Government's 2050
aspiration, it is important first to understand the contribution that transport currently
makes to UK emissions.
2.2 In this chapter, we set transport within the context of other UK sources of emissions,
highlight the main elements of transport emissions by mode and summarise the trends
that have defined transport emissions in recent decades.
2.3 The chapter ends with an overview of some of the factors that lie behind trends to date
and might be material in future, before going on in Chapter 3 to consider opportunities
for reducing transport's carbon emissions over the long and shorter terms.
Transport accounts for between one-quarter and one-third of UK emissions
2.4 The exact share of UK transport-related emissions of carbon dioxide depends on how
emissions are apportioned across sectors in the economy, and whether international
aviation and shipping are included in the figures.
2.5 The first distinction is between 'end-user' or 'source' figures. End-user figures include
an estimated share of upstream emissions from power stations and refineries allocated
back to the sectors using the electricity or fuel (sometimes referred to as 'well to wheel').
Source figures allocate emissions according to where the fuel (e.g. coal, gas, oil, petrol
etc.) is consumed and so do not attribute emissions arising from fuel refining or electricity
generation to the transport sector but to the energy sector.
2.6 Total UK emissions in both cases are the same (151.7 MtC in 2005, not including
international aviation and shipping), but the difference for individual sectors can be
substantial. Transport sector figures increase from 35.2 to 41.6 MtC, with the sectoral
share of the total rising from 23% to 27%, once upstream emissions are reallocated
(Defra, 2007b).
2.7 The second distinction is between domestic and international emissions. Government
targets, projections and modelling usually exclude emissions from international aviation
and shipping, as there is no agreed convention on how to allocate these emissions to
individual countries. For instance, the UK's Kyoto target does not include emissions
from these sectors, with responsibility for regulating emission levels within international
shipping and aviation passing to the International Maritime Organisation and the
International Civil Aviation Organisation.
2.8 A truer picture of the UK's emissions would include at least some emissions from these
international movements. Using a method of calculating aviation and shipping emissions
based on fuel used in 'international bunkers', this would add 11 MtC to the normallyreported
figures, increasing transport's share to 28% (46.3 MtC, as source) or 32% (52.7
MtC, as end user) of an expanded UK total for carbon emissions. It would mean that air
traffic would account for approximately 6% (9.5 MtC) of total emissions by source.
2.9 These figures exclude the additional effect of other greenhouse gases and atmospheric
effects including those caused by air travel at high altitudes. Scientific studies have
identified other climate effects in the upper atmosphere, linked to the emissions of
nitrogen oxides, particles and water vapour - and similar effects may also arise from
ground-based emissions sources. Research continues to assess how much warming is
caused by aviation emissions at high altitudes, as the science is still much more
uncertain in this area than for CO2 and the other greenhouse gasses identified in the
Kyoto protocol. In addition, these upper-atmosphere effects are much more short-term
than the warming impact of CO2 that continues for hundreds of years.
2.10 Some studies have attempted to express these upper-atmosphere impacts of aviation
as a multiple of its CO2 emissions, using an index of radiative forcing (RFI). On this basis,
IPCC (1999) estimated that the total climate change impact of aviation emissions to
2050 would be 2.7 times the carbon dioxide impact, though more recent research has
reduced this figure to a central estimate of 1.9 (Sausen et al., 2005). Scientific uncertainty
places a wide band around both estimates. But, just as important, the short-term nature
of the non-CO2 global warming impacts means that these multipliers are very sensitive
to the time period considered. Forster, Shine and Stuber (2005) show that the IPCC
central estimate of a multiplier of 2.7 could increase to 3.7 if a 20-year time horizon was
considered, but would fall to 1.2 using a 500-year time horizon. For this reason, great
care needs to be taken when applying these RFI multipliers in a policy context, as the
European Commission recognised in its recent proposals to include aviation in the EU
Emissions Trading Scheme.
Source: Defra, 2007b[1], [2].
2.11 Depending on whether 'end-user' or 'source' figures are used, transport thus accounts
for between approximately a quarter and one-third of UK carbon emissions. At the
higher figure (end-user and including international transport), transport is the largest
single sector for UK emissions.
2.12 A further way of presenting the figures is to consider emissions at the level of households:
Exhibit 2.1 uses official data to show that transport accounts for a large share of
household GHG emissions, though energy use in the home and indirect emissions
associated with household purchase of other goods and services account for larger shares.
Exhibit 2.1
Household total greenhouse gas emissions (2001)
The energy used directly by households through cooking, heating and using their
own vehicles, and indirectly by the generation of electricity, through the use of
public transport, taxis and aircraft and from households' final demand for goods
and services (which include emissions embedded in imports of goods and
services), amounts to around 85% of all UK GHG emissions (ONS, 2004).
Personal transport is an important part of this. The Office of National Statistics
(2004) estimated total GHG emissions from UK households' personal use of
transport at 29.3 MtCO2 eq. approximately 15% of all UK emissions. This
comprised emissions from private vehicles (17.7 MtCO2 eq.), aviation (here
including international aviation, counting only the outbound trip - 8.9 MtCO2 eq.)
and public transport (2.8 MtCO2 eq.).
Source: ONS, 2004.
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2.13 We believe it more appropriate to refer to end-user figures, as they provide the most
complete account of the relationship between emissions and transport, but this
classification is subject to more uncertainty than source figures, for which data are more
accurate and readily available. Carbon savings attributed to policy instruments discussed
later in this report are available as source figures, and so, hereafter, we refer to source
emissions and do not include international movements unless otherwise indicated.
Road transport is the main source of transport emissions
2.14 Road transport is the most significant producer of greenhouse gases in the transport
sector, accounting for 93% (about 33 MtC) of domestic transport emissions by source.
Cars make up over half of these emissions, with large goods vehicles (lorries) and vans
together responsible for just over a third[3]. Flights within the UK are currently responsible
for 2% of domestic transport emissions, equating to 0.4% of UK total carbon emissions.
Including international air travel would increase aviation's share of transport emissions to
over one-fifth (see also Figure 2.4).
Source: Defra, 2007b[4], [5].
Transport emissions have risen since 1990, while total UK emissions have fallen
2.15 Although other sectors (e.g. residential) have experienced increases in emissions in
recent years, transport is the only sector in which carbon emissions were significantly
higher in 2005 than in the Kyoto baseline year of 1990 - partially offsetting reductions
made elsewhere in the economy (Figure 2.3). Total UK emissions of CO2 fell by 6%,6
while transport emissions grew by almost 11% (not including international movements).
Source: Defra, 2007b.
Aircraft and goods vehicles are among the fastest-growing sources of transport emissions
2.16 Within transport as a whole, emission trends since 1990 have differed for individual
modes (Figure 2.5, which unlike Figure 2.4 includes international transport). While cars
are the most significant mode, their emissions have stabilised at roughly 1990 levels,
despite an 18% increase in car traffic over this period (DfT, 2006a). Public transport
emissions have fallen by 9%[6] since 1990, though this has had marginal impact overall,
given public transport's small share of the market (notwithstanding recent growth in
rail patronage)[7].
2.17 Aviation emissions have grown fastest of all. Since 1990, domestic aviation has seen
emissions growth of nearly 100%; international air travel emissions have grown by 123%
(based on figures for fuel used in 'international bunkers' and calculating the emissions
related to the burning of this fuel). It is worth noting that dedicated freight aircraft only
represent around 3% of total aircraft movements at all UK airports: approximately twothirds
of airfreight tonnage is carried in the cargo space of passenger aircraft.
2.18 According to Defra statistics, use of vans has resulted in steep growth in emissions, up
nearly half since 1990 so that they now account for 13% of domestic transport emissions.
Lorries currently account for 22% of transport emissions and have grown by almost a
third over the same period. However, research carried out for CfIT (McKinnon, 2007)
has shown that trend emissions figures for lorries and vans can vary by a factor of 3[8], depending mainly on whether bottom-up surveys of road freight activity and fuel
efficiency or top-down sectoral estimates of fuel purchases are used. The above figures
seem to be based on the latter, which may overestimate emissions growth from these
modes. Crucially, the Defra figures appear to be reporting increases from the road haulage
sector alone, which will have been offset by reductions in transport in other sectors
particularly as many vehicle fleets were contracted out over the period in question. It
is also worth noting the lack of clarity about the proportion of distance travelled by vans
that can be considered as 'freight'. McKinnon estimates[9] that freight - the collection
and/or delivery of goods and associated empty running - may be as low as 35% of van
kilometres, the remainder being accounted for by commuting and by small businesses
such as builders.
Source: Defra, 2007.
2.19 Emissions from shipping present an interesting picture, albeit once again confused by
the different ways of accounting for fuel use and apportioning emissions across countries.
Globally, shipping has been estimated to account for between 1.8% and 3.5% of global
CO2 emissions (CE Delft, 2006 cited in DfT, 2007c). Recent reports highlight that CO2
emissions from shipping are double those of aviation and increasing rapidly (Guardian,
3 March, 2007). Others, based on fuel sales in the EU-27, show that carbon emissions
from marine and aviation are about the same (Concawe, 2006). However, unlike aviation,
emissions from sales of UK shipping fuels (bunker fuel) appear to have fallen by about
12% between 1990 and 2005. This is against a background of significant growth in the
amount of freight passing through UK ports since 1970 and the fact that some 95% of
the UK's international trade in goods travels by sea (DfT, 2006a and 2007c).
2.20 While the fall in emissions from sales of UK shipping fuel may be partly due to improved
efficiency (such as from the general trend towards larger vessels and improvements to
engine efficiency), another factor may be the practice of most UK shipping operators of
purchasing much of their fuel outside the UK, even when they carry a considerable
amount of freight to and from the UK. In addition, much of the world's bunker consumption is accounted for by the large tankers and bulk carriers, and the distances involved allow
the long-range ship owner flexibility when choosing a refuelling location. As fuel price
varies throughout the world, ships will thus often fill up at locations supplying cheaper fuel,
creating inconsistent national variations in the marine bunker fuel purchased each year.
2.21 By contrast, the UK is a major hub for aviation. The competitive nature of fuel supply at
UK airports may mean a disproportionate amount of fuel (kerosene) may be being sold
here, particularly for short-haul flights to Europe that do not need refuelling on every trip.
Although there is no evidence to support this, it does highlight the risks in assuming the
bunker fuel purchased within a particular nation approximates to its share of shipping or
aviation emissions.
Many factors help explain transport emissions trends
2.22 Transport emissions arise from the use of motorised transport powered by fossil fuels
(e.g. petrol, diesel, gas or electricity generated from fossil fuels such as coal or gas) and
are essentially a function of four things:
- the demand for movement, itself derived from the need to access facilities, services
and goods;
- the mode of transport used to meet that demand;
- the combined technical efficiency of vehicles and the carbon content of the fuels used
to power the vehicles; and
- the operational efficiency with which vehicles are used (e.g. how they are driven and
how much of their carrying capacity is used).
2.23 Each of these areas in turn is influenced by a wide range of factors that help explain
transport emissions trends to date and will shape such trends in future. Some factors
will serve to contain or reduce emissions; others will have the opposite effect. A number
of the more important factors are set out below.
Economic growth
2.24 Traditionally, transport activity, economic activity and carbon emissions have been
strongly correlated (Banister and Stead, 2002). As incomes grow, the demand for travel
increases, as does the demand for goods and services. These trends can be influenced
by individual preferences as well as social and cultural norms that have an impact on
journey purposes (e.g. more travel for leisure), journey lengths and modes used - we
travel further and faster, choosing to purchase vehicles with greater power and additional
features, thus increasing weight and off-setting efficiency gains.
2.25 Changes in the nature of economic activity (themselves sometimes facilitated by changes
in transport) can also affect the demand for transport. Specialisation of production,
globalisation and the growth of trade - trends set to continue in future - have also
seen increased movement of goods and services.
2.26 The type of land use that accompanies economic growth is also important. The trend towards centralisation of services, distribution and retail provision often at edge of town
developments, together with less dense housing provision, have all contributed towards
increasing demand for transport[11].
2.27 Nevertheless, there are signs that the historic correlation between economic growth and
road traffic growth may be changing. Between 2000 and 2005, traffic was recorded to
have grown by 7% overall (5% for cars only) (DfT, 2006a) which is significantly less than
was expected in the Transport White Paper (DfT, 2004b). Going forward, the overall
demand for road transport is predicted to slow, with a 31% increase expected between
2003 and 2025, implying an annual growth rate of 1.2% per year (Eddington, 2006).
However, within this van traffic is expected to increase most rapidly with expected growth
of 70% over the period, in line with recent trends.
Demographic change
2.28 The last fifty years have seen some dramatic changes to the socio-demographic structure
of Great Britain. In 2004 there were 7.0 million people living alone in Great Britain, nearly
four times as many as in 1961. Over the same period, the average household size has
declined from 3.1 to 2.4, while the number of households has increased by 7.8 million.
There has also been a marked increase in the number of women in the workplace, and
63% of women now hold a full driving licence, up from 29% in 1975/6 (DfT, 2006a). And
while only three out of ten households in Great Britain in 1961 had a car, by 2004, one in
four households did not have a car, whilst almost one in three had two or more (DfT, 2006a).
2.29 The UK's demographic structure is expected to change significantly in future, in particular
through an increasingly ageing population. Although much modelling assumes this will lead
to a slow-down in traffic growth, it could lead to an increase as, unlike past generations,
these older cohorts may have higher incomes, will have grown up being dependent on the
car and may have a higher propensity to travel by air. For example, of those aged over
70, over half hold a driving licence (51%) compared to only 15% in 1975/6 (DfT, 2006a).
Costs of transport
2.30 The overall costs of motoring have fallen in real terms in last 20 years. In addition, over
this period increases in public transport fares above the rate of inflation have also made
travel by car relatively cheaper - hence strong growth in private road transport over the
long term.
2.31 The demand for petrol-based transport can be dampened, as occurred with the
introduction of the Fuel Duty Escalator in 1993 (later removed in 1999), which reduced
emissions below what otherwise would have been: the Government estimates it will
continue to save 1.9 MtC annually to 2010, making it one of transport's key contributors
to the UK Climate Change Programme (see Chapter 3). Fuel tax can encourage some
motorists to lower the fuel duty they pay without necessarily reducing mileage, by
switching to more-efficient cars. In recent years this has meant primarily diesel cars which,
taking a medium sized car, on average produce around 13% less CO2 per kilometre than
a petrol equivalent (Defra, 2007d).
2.32 Since deregulation of the airline industry in 1996, the development of the low-cost
aviation sector has significantly altered the way the short-haul airline market operates.
In particular, this development has introduced low and unrestricted fares and has opened
up the range of destinations and airports available. The DfT suggests 'this increasing
desire and propensity to fly can be explained by the growing affordability of air travel'
(DfT, 2006b, p25). Research commissioned by CfIT found that recent reductions in the
price of flying has stimulated the growth in flying (being given as the single biggest factor
why people are flying more for leisure than they did five years ago) (Ipsos MORI, 2007 -
Exhibit 2.2).
Exhibit 2.2
Ipsos MORI survey on attitudes to aviation and climate change - results on flying behaviour
Ipsos MORI conducted 1122 face-to-face interviews and a one-and-a-half-day
deliberative event involving members of the public with stakeholders from the
aviation industry, environmental lobby and academia in order to discuss flying
behaviour. The research showed:
- consistent with previous research studies, over 40% of people in England have
flown for leisure in the past 12 months;
- while the majority have flown just once, nearly a quarter of those who have flown
(23%) have done so three or more times;
- frequent flyers (3+/year) are more likely to have increased their air travel since five
years ago, with over 60% flying more often;
- in line with forecasts, the majority of people expect to fly as often or more
frequently in the future (82%), with half of those who have not flown in the past
year expecting to fly at some point in the future;
- only a small proportion (11%) expect to fly less frequently in the future, and this
is predominantly due to changes in personal circumstances rather than a
concern about the environmental impact of aviation.
Source: Ipsos MORI, 2007.
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2.33 There is, however, some debate as to whether the low-cost sector has led to an
increase in the overall passenger growth rate or whether the growth in that sector has
been at the expense of established full-service scheduled carriers and charter flights -
i.e. it may well have happened anyway, particularly because of income growth (CAA,
2006). The evidence is uncertain, since it is difficult to know what would have happened
in the absence of the restructuring of the industry. Since 1996, annual growth rates have
averaged around 5-6%, which represent strong growth but are similar to the rates
experienced prior to deregulation[12].
2.34 What is clear is that most of the current air-passenger demand is for leisure purposes
and the availability of low cost flights has not in fact significantly altered the type of
people who are flying (Dargay et al., 2006; CAA, 2006). The growth is made up of
existing passengers flying more than in the past, particularly those from middle and
higher income bands travelling short-haul. CfIT-commissioned survey work also found
the frequent flyers (3+/year) are more likely to have increased their air travel compared
to five years ago, with over 60% flying more often (Ipsos MORI, 2007).
Network developments
2.35 Improved transport networks, such as completion of the railway and motorway systems,
or development of international and domestic air links, can also encourage growth in
transport. There have been points in time when different travel modes have become
faster, cheaper, safer and more comfortable, allowing people to travel further within a
constant 'travel time budget', even if the benefits of improvements have not always been
sustained over time.
2.36 This demand for more speed, power and comfort has eroded some of the efficiency gains
that would on their own have led to a reduction in emissions per kilometre travelled. On
the other hand, some of the benefits of network improvements are being countered by
growing congestion on different modes - something which may or may not be addressed
in future by measures aimed at managing demand.
Vehicle/fuel technology and operational efficiency
2.37 Previous decades have seen significant improvements in the efficiency of various
vehicle/fuel technologies. Average new (two-wheel drive) petrol car efficiency, for example,
has improved by around a quarter since the late 1970s (DfT, 2006a). The share of diesel
reached 36% of the new car market in 2005. Diesel cars now account for 21% of the
overall car fleet, up from under 9% in 1995. Aircraft fuel efficiency per passenger
kilometre has improved by over 40% in recent decades (SITA, 2006).
2.38 Such improvements are positive ones in terms of addressing transport emissions, but
their ultimate impact may reduce over time. Improved fuel efficiency in cars has worked
to stabilise emissions from cars at roughly 1990 levels, despite an 18% increase in road
traffic over this period. However, one effect of vehicles becoming more efficient is to
reduce the unit cost of travel, partly stimulating increased mileage and the purchase
of larger and heavier vehicles, thus partly offsetting the original beneficial effects. This
phenomenon of increased travel resulting from efficiency savings is often referred to
as the 'rebound effect'.
2.39 Looking forward, further improvements in road vehicle fuel technology are anticipated,
which are due to continue to stabilise emissions from this sector. More significant
developments in vehicle and fuel technologies are also expected to deliver further gains
in tackling carbon emissions - see Exhibit 2.3.
Exhibit 2.3
Future road vehicle and fuel technologies
Road transport is widely expected to be dependent on oil for several decades to
come, but significant changes are anticipated.
The market for diesels in the UK is expected to continue to grow over the next few
years, perhaps eventually achieving a market penetration of around 60% (PWC, 2006).
Cleaner fuels that provide tangible emissions benefits are being developed, and
these can be used in conventional internal combustion engine (ICE) vehicles, such
as the use of biofuels.
A second strand is the development of alternative vehicle technologies that partially
or completely replace conventional engines. This process has already begun with
the introduction of the hybrid vehicle, which combines the advantages of the ICE
with an electric drive train. Hybrid technology (micro, mild and full) will increasingly
be used by automotive manufacturers to reduce CO2 emissions. Enhanced power
systems, combined with regenerative braking, will make better use of engine
power, allowing improved environmental performance and/or engine downsizing.
Hybrid technology can be combined with renewable fuel technology to reduce real
world emissions further.
Hybrids are developing rapidly with a dominant system of design yet to emerge.
Figures from SMMT show that 8957 petrol/electric cars were newly registered in
2005, and 298 all electric vehicles, up from zero in 2005 (SMMT, 2007c).
Hybridisation of vans and medium-duty trucks is also expected to see rapid
development over the next decade.
Pure electric vehicles using batteries have been available for many decades but
have suffered major drawbacks in terms of performance, range, recharging times
and availability of recharging infrastructure. Improved battery technology is allowing
greater mileage between charges and higher speeds in vans as well as cars (PWC,
2006). However, this technology is only zero-emission at the tailpipe and its real
climate change benefit is very much linked to the way in which the electricity is
produced in the first place (SMMT, 2006).
Hydrogen is seen by many as a potentially dominant fuel, either burnt in a
conventional engine or by producing electricity to run a car through a fuel cell.
However, hydrogen is a carrier, rather than source of energy, and although the only
emission is water at the tailpipe, lifecycle emissions depend on how the hydrogen
is produced. There are also big challenges to changing our transport structure over
to hydrogen, as it is difficult to store and transport in bulk and needs a lot of energy
to produce. Consequently, although hydrogen and fuel-cell cars are available now
in prototype, this technology is still several decades away from being commercially
available in the UK.
Sources: PWC, 2006; SMMT, 2006 and 2007c.
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2.40 In the case of aviation, the central-case forecast produced by DfT to support its 2003 Air
Transport White Paper assumed aviation fuel efficiency would improve by 50% between
2000 and 2050, resulting from both better engine and airframe design, and operational
improvements (DfT, 2004a). The UK aviation industry has made a commitment to improve
fuel efficiency by 50% per seat kilometre, including up to 10% from air traffic management
efficiencies (AOA, BATA, SBAC and NATS, 2005). However, most scenarios of aviation
and emissions growth show that the growth in air travel is likely to outstrip the rate of
improvement (see Chapter 3 for emissions growth projections).
2.41 It is also important to note that different carbon efficiencies exist between modes of
transport. These differences can be explained by the different technology deployed,
vehicle size and capacity, technical standards, or indeed topography or weather
conditions. Each mode is also restricted to a specific network, and each network (road,
rail, sea and air) has its own unique characteristics that can affect vehicle operation and
efficiency. Comparative figures are difficult to produce, given the variety of assumptions
involved regarding average vehicle type, driving styles and occupancy rates. Figure 2.5
displays Government reporting guidelines using a set of assumptions found in Defra
figures (2007c).
Source: Defra (2007c) Guidelines to Defra's GHG conversion factors for company reporting: annex updated June 2007.
Conclusions
2.42 Using the most appropriate basis of measurement, transport is now the largest single
source of emissions in the UK, within which road transport is the main component and
of which in turn cars are the most significant element.
2.43 In the UK, transport has been the only sector whose emissions grew significantly
between 1990 and 2005, a period in which reductions in other sectors of the economy
saw total UK carbon emissions fall by 5% (Defra, 2007e).
2.44 Emissions from air travel and from the movement of vans and lorries in turn have been
among the fastest-growing sources of transport emissions in the UK. Emissions from
cars have been stable since 1990, while those from public transport have fallen.
2.45 There is a need for improved data and understanding related to emissions from shipping,
and from the use of lorries and vans.
2.46 There are many factors behind transport emission trends to date, including the demand
for transport, mode choice, vehicle/fuel technology and the efficiency with which different
forms of transport are used.
2.47 Technological improvements have delivered benefits in terms of carbon reduction, but
these have either been offset (in the case of car use) or out-stripped (in the case of air
travel) by rising demand and choices made by transport users - these trends are set to
continue in future.
2.48 These insights underline the importance of looking at how to cut transport's carbon
emissions if the UK is to meet its goals for overall carbon reduction - and action to
stimulate further technological improvement, as well as behavioural change, will be vital.
2.49 However, these insights in themselves indicate neither the scale of reduction in transport
emissions, nor the type of appropriate measures, that would be consistent with a costeffective
UK-wide programme to deliver major carbon abatement. The following chapter
seeks to review the relevant state of knowledge on these issues.
1: Energy industry includes: energy industry and fugitive emissions from fuels; commercial/public sector includes: commercial and institutional, military aircraft and shipping, waste (and exports in the case of 'end user'); industrial includes: manufacturing industry and construction and industrial processes.
2: Figures for international aviation and shipping emissions are only available 'by source' and have been added to total end user emissions as an estimate.
3: However, figures for carbon emissions from freight traffic can vary according to their method of collection. See research undertaken for this study by McKinnon for alternative figures on freight CO2 emissions (McKinnon, 2006).
4: As this is by source, it excludes the emissions from electricity generation in rail.
5: Note the difference between CO2 emissions and total greenhouse gas emissions here. The total basket of 'Kyoto' greenhouse gas emissions fell by 15.6% between 1990 and 2005 (Defra, 2007d). However, most recent estimates show carbon emissions rose again during 2006, mainly due to fuel switching from natural gas to coal, so that the level is currently only around 5% below the base year (Defra, 2007e).
6: This is made up of carbon emissions from buses reducing by 23% (despite +13% increase in bus and coach kilometres since 1990 (TSGB)) and railway emissions increasing by 50%.
7: In 2005, 85% of passenger kilometres were undertaken by car, van or taxi, 6% by bus and coach, 6% by rail and the remainder by motorcycle, bicycle and domestic air travel (DfT, 2006a).
8: A recently published Defra document claims that CO2 emissions from lorries rose by 29% between 1990 and 2004. This figure is more than three times higher than the estimate based on the Continuing Survey of Road Goods Transport and National Road Traffic Survey (see McKinnon (2007) for further discussion).
9: Using results of the 2004 Survey of Van Activity (DfT, 2004c).
10: 'Other' includes motorcycles and mopeds; LPG emissions; other road vehicles and mobile sources and machinery. International shipping and aviation have been calculated using fuel in international bunkers.
11: CfIT (2006). Sustainable Transport Choices and the Retail Sector. London: CfIT.
12: See Dargay and Cairns (2006) for a discussion of growth rates over this period. Certain years since 1996 saw increased growth rates and others, particularly after the September 11 attacks, saw slower growth rates.
13: Figures for private vehicles based on average values for UK car fleet in 2005 and use a 15% uplift factor for 'real word' conditions (UK average car occupancy of 1.6). Bus data based upon all bus class and journey data from the UK GHG inventory and an average load factor of 9.2. Air emissions include a 9% uplift factor but do not include the additional impacts of radiative forcing (e.g. non-CO2 impacts). Note the Defra document does not include figures for shipping. It has been reported that shipping can be up to 4-5 times more carbon-efficient than road transport per tonne kilometre (Wahlström et al., 2006).
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