Carbon Account For Transport No. 3: 2011/12 Edition

Chapter 2: Background emissions analysis

2.1 Background

The emissions data presented in this chapter are from the 'Greenhouse Gas Inventory for England, Scotland, Wales and Northern Ireland: 1990-2009'[9] (GHGI) unless stated otherwise. The GHGI is compiled on an annual basis and the full time series of all greenhouse gases is updated in each publication to take account of improved data and any advances in calculation methodology. The greenhouse gases associated with transport and recorded by GHGI are Carbon Dioxide (CO2), Nitrous Oxide (N2O) and Methane (CH4)[10].

The transport category within the GHGI covers emissions from road, aviation, rail and maritime transport. While domestic aviation and shipping emissions are reported in the GHGI, emissions associated with international aviation and shipping are not. However, using existing data sources, an indicative assessment of the emissions from international aviation and shipping from each country in the United Kingdom was first published in 2009 and continues to be published as an appendix within the annual GHGI publication. Consequently, in line with the Scottish Government commitment to include emissions from international aviation and international shipping within the targets set by the Climate Change (Scotland) Act, references to aviation and maritime emissions in this document refer to both domestic and international, unless otherwise stated.

The transport emissions reported only cover emissions at the point of use (tailpipe emissions). Consequently, no lifecycle impacts within the transport infrastructure and no displaced impacts, such as the emissions generated by the electricity used on electrified railways, are included.

2.2 Historic Emissions Trends

Transport in Scotland produced 13.6 mega-tonnes of carbon dioxide equivalent (MtCO2e) emissions in 2009. This total represents a 0.7 MtCO2e or 4.8% fall from the equivalent 2008 figure, and the second consecutive year of annual reduction in transport emissions. 2009 emissions are though still some 3.7% above the 1990 base year emissions total of 13.1 MtCO2e. The global recession has clearly played a significant part in the recent reduction in reported emissions but movements in transport emissions are in addition affected by car ownership levels, global oil prices, household income, population, land planning and use, public transport provision and culture and lifestyles.

The recession has also affected emissions from all other sectors. The falls seen elsewhere have, in proportionate terms, been greater than in transport so the percentage of Scottish emissions accounted for by the transport sector increased between 2008 and 2009. This continues the trend of transport contributing an increasing proportion of annual Scottish emissions: the sector now accounts for over 21% of total emissions if International Aviation and Shipping (IAS) emissions are excluded, and just below 26% with the inclusion of IAS emissions.

Figure 1: Total emissions from transport and transport emissions as a percentage of total Scottish emissions, 1990-2009

Figure 1: Total emissions from transport and transport emissions as a percentage of total Scottish emissions, 1990-2009

Source: Greenhouse Gas Inventory, NAEI, 2011, Transport Scotland. Total emissions exclude the impact of the EU Emissions Trading System

Emissions by mode

With the exception of a marginal increase in rail emissions, all broad modes of transport saw emissions reductions between 2008 and 2009:

  • Emissions from cars and motorbikes fell by 0.15 MtCO2e;
  • Emissions from lorries and vans fell by 0.22 MtCO2e;
  • Emissions from IAS fell by 0.20 MtCO2e; and
  • The other sectors combined provided the remaining 0.11 MtCO2e of emissions reductions.

Figure 2: Transport emissions 1990-2009 broken down by broad transport sector

Figure 2: Transport emissions 1990-2009 broken down by broad transport sector

2.3 Analysis by transport sector

Road transport

Road transport emissions cover emissions from all private, public and commercial road vehicles. Together, this category accounts for around 70% of all transport's emissions, with cars alone accounting for 60% of road transport emissions.

Emissions from road transport fell by just under 4% between 2008 and 2009, from 9.9 MtCO2e to 9.5 MtCO2e. They are now more than 6% below their 2007 emissions peak of 10.2 MtCO2e. Overall, road emissions in 2009 were just over 3% higher than their equivalent 1990 figure. Road emissions as a percentage of total transport emissions rose slightly in 2009. Within the road transport sector HGV emissions fell at a rate greater than the overall rate of reduction in road emissions (falling by 9%) while car and LGV emissions, the two other significant components of road transport emissions, each fell by between 2% and 3%.

Figure 3: Road transport emissions 1990-2009 and as a share of total transport emissions

Figure 3: Road transport emissions 1990-2009 and as a share of total transport emissions

Further analysis of road transport emissions is undertaken in section 2.4.

Maritime transport

Maritime emissions[11] in 2009 are estimated to be 2.1 MtCO2e, just less than 16% of total transport emissions in that year. As international shipping accounts for between 75% and 85% of the sector's total emissions, so the performance of the maritime category is principally driven by changes in this one activity. Historically, maritime emissions, and international emissions in particular, have been very volatile. Between 1995 and 2002 shipping emissions fell by 40% to 1.7 MtCO2e before rising again by over 30% to 2.3 MtCO2e by 2008. International shipping emissions fell by over 7% between 2008 and 2009 which, when coupled with smaller falls in emissions from the other components of maritime transport, lead to an overall fall in maritime emissions of 7%.

Figure 4: Maritime emissions 1990-2009 and as a share of transport emissions

Figure 4: Maritime emissions 1990-2009 and as a share of transport emissions


Aviation emissions in 2009 are estimated to be 1.7 MtCO2e and account for just under 13% of total transport emissions. At their peak in 2007 emissions from this category accounted for over 14% of all transport emissions. International aviation emissions make up the majority of this category's emissions (60%).

Overall aviation emissions fell by over 8% between 2008 and 2009 but remain some 0.6 MtCO2e above their 1990 figure, driven almost exclusively by an increase in international emissions over the period. The reduction in recorded aviation emissions between 2008 and 2009 has been driven by large falls in the domestic and military aviation emissions (12% cruise, 13% take off and landing, 14% military) while international emissions have fallen by 5% over the same period.

Figure 5: Aviation emissions 1990-2009 and as a share of total transport emissions

Figure 5: Aviation emissions 1990-2009 and as a share of total transport emissions


Rail emissions rose by 6% between 2008 and 2009 and the 2009 emissions total of 0.2 MtCO2e is 27% above the equivalent 1990 figure. Despite these shorter and longer term increases in rail emissions the sector still accounts for less that 2% of all Scottish transport emissions.

Figure 6: Rail emissions 1990-2009 and as a share of total transport emissions

Figure 6: Rail emissions 1990-2009 and as a share of total transport emissions

2.4 Road Emissions by vehicle type

Cars: At 5.6 MtCO2e in 2009, emissions from cars account for both the greatest proportion of road emissions as well as all transport emissions; 60% and 41% respectively. Emissions from cars have fallen slowly from a peak of 6.2 MtCO2e in 2002 to their current level so that they are now 9% below that peak figure and also 0.2 MtCO2e below their 1990 level.

HGVs: Emissions from HGVs make up the second largest proportion of road emissions. HGV emissions in 2009 were just under 1.9 MtCO2e, a 9% reduction on the 2008 figure of 2.1 MtCO2e. After a run of six years of continuous years of emissions growth between 2002 and 2007 falls in both 2008 and 2009 mean emissions from this vehicle type are at their lowest annual level since 2004, and are now below the 1990 base year level of 2.1 MtCO2e.

LGVs: LGV emissions fell by 2.6% between 2008 and 2009 from 1.4 MtCO2e to 1.3 MtCO2e. Emissions have now fallen for the last two years having risen steadily between 2001 and 2007. Despite this fall, the latest emissions figure for LGVs is 70% above the base year total of just under 0.8 MtCO2e.

Buses and motorcycles: Emissions from buses fell marginally between 2008 and 2009 (<0.01 MtCO2e) and remain just over 0.6 MtCO2e, while motorcycle emissions remain stable at just under 0.05 MtCO2e.

Figure 8 shows the year on year percentage change in the three largest road emitting categories. All three categories have seen recent reductions in emissions and, in the case of commercial vehicles this has reversed a trend of increasing emissions in at least the preceding six years. The sharp reversal in trend is undoubtedly in part a consequence of the economic recession.

Figure 7: Breakdown of Road Emissions by Vehicle Type 1990-2009

Figure 7: Breakdown of Road Emissions by Vehicle Type 1990-2009

Figure 8: Year on year change in car, HGV and LGV emissions 1995-2009

Figure 8: Year on year change in car, HGV and LGV emissions 1995-2009

Emissions by road type

The GHGI database also differentiates road transport emissions across three road types: rural, urban and motorway. Just over half of Scottish road emissions arose from rural driving in 2009, a small reduction in percentage terms from the position in 1990. Urban emissions have remained at or just under one third of emissions and it is only emissions from motorway driving that have shown any real change over the period. Emissions from motorway driving in 2009 are some 38% higher than in 1990. All three categories registered slight falls in emissions between 2008 and 2009.

Figure 9: Breakdown of road emissions by road type 1990-2009

Figure 9: Breakdown of road emissions by road type 1990-2009

2.5 Comparison of key Scottish and UK Transport emission figures and trends

Table 1: Comparison of Scottish and UK GHG emissions
  Scottish Emissions 2009 Scottish Emissions 2009 as a % of UK emissions Change in Scottish Emissions (2008-9) Change in UK Emissions (2008-9) Change in Scottish Emissions (1990-2009) Change in UK Emissions (1990-2009)
All Transport 13,577 8.2% -4.8% -4.4% 3.7% 12.8%
All Transport  (excl. IAS) 10,742 8.8% -4.3% -4.2% 1.7% 0.0%
Road Transport 9,515 8.4% -3.8% -4.0% 3.7% 2.2%
of which:
Cars 5,620 8.0% -2.8% -2.8% -3.3% -3.0%
HGVs 1,896 9.1% -8.7% -9.1% -9.1% -12.8%
LGVs 1,342 8.8% -2.6% -3.2% 69.1% 61.8%
Buses 610 11.5% -0.4% -1.1% 41.2% 38.8%
Motorcycles 47 7.4% 1.6% 1.6% -8.4% 1.7%
Rural 4,801 10.7% -3.6% -4.4% -1.0% 0.4%
Urban 2,991 7.0% -3.7% -3.3% -2.9% -5.2%
Motorway 1,673 6.6% -4.6% -4.5% 37.6% 19.8%
Rail 210 9.6% 6.1% 1.8% 27.2% 4.9%
Aviation 1,719 4.7% -8.2% -5.2% 55.0% 75.1%
Maritime 2,132 16.6% -7.1% -6.8% -19.3% 4.7%

Scottish transport emissions including IAS currently account for 8.2% of total UK transport emissions and 8.8% of emissions if IAS is excluded. Emissions from road transport in Scotland are in proportion to the overall UK figure while the aviation (4.7%) and maritime (16.6%) sectors show the greatest variation from the equivalent UK figure.

Within the category of road transport it is only for buses and motorcycles, the smallest sub-categories in respect of emissions, where the Scottish share of emissions varies significantly from the overall percentage. Historically, all sub categories of Scottish road transport emissions have move in line with the equivalent UK level series. By road type, there are proportionally more emissions derived from rural roads in Scotland and proportionally fewer from both urban roads and motorways.

It is the difference in size and change in emissions from the aviation and maritime sectors that have driven the change in overall transport emission performance between Scotland and the UK, particularly in respect of the changes seen between 1990 and 2009. Excluding IAS UK emissions in 2009 are at the same level as 1990, with Scotland seeing a small increase of less than 2%. However, once emissions from IAS are included the position changes significantly. UK emissions in 2009 are 19 MtCO2e above their 1990 level, an increase of just under 13%. In Scotland the rise is only 0.5 MtCO2e, an increase of less than 4%. More specifically, while international aviation emissions have more than doubled at the UK and Scottish level, international shipping emissions have risen by 16% at the UK level but fallen by 14% in Scotland. This sub-UK level change is due in significant part to a reallocation of emissions between UK countries. With international aviation emissions making up around three-quarters of total UK IAS emissions but only just over a third of Scottish IAS emissions (with maritime consequently being far more important to the Scottish IAS figure) the drivers behind the changes in transport emissions including IAS are more obvious.

2.6 Efficiency of passenger vehicles

Different modes of transport have the capacity to transport different numbers of passengers. For example the average number of passengers on a bus is higher than the average number of passengers in a car. As such the efficiency of transport modes, in terms of the CO2 per passenger kilometre transported, varies. Defra's Company Reporting Guidelines[12] allow comparisons to be made between the emissions per passenger kilometre[13] of different modes of travel.

Table 2: CO2e emissions per passenger kilometre by mode
Sector Mode gCO2e/pkm
Road[14] Average petrol car 131
Average diesel car 121
Average petrol hybrid car 87
Average petrol motorbike 116
Average bus 149
Average coach 31
Rail National rail 57
Light rail and tram 72
Ferry (Large RoPax) Average foot and car passengers 116
Aviation Domestic flights 163
Short haul international 96
Long haul international 110

Source: 2010 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting: Methodology Paper for Emission Factors. August 2011.

All values shown in Table 2 are estimated using data for Great Britain so do not specifically relate to Scotland. In general, public passenger transport (rail, coach, tram) are more efficient in terms of CO2e/pkm because they transport more people at one time.

2.7 Leading indicators

Data on greenhouse gas emissions tends to lag approximately a year behind other transport data. Consequently, in order to keep the information in the CAT as relevant as possible, the following indicators provide some insight into likely future trends in GHG emissions:

  • Road vehicle kilometres travelled: Emissions are directly related to the kilometres travelled. This indicator tracks vehicle kilometres travelled by all vehicle types on all roads.
  • Road transport fuel consumption per vehicle kilometre: Fuel efficiency in this context relates to reducing fuel consumption in road transport without impinging on our ability to transport ourselves. Holding all else constant, the more fuel efficient we are as we travel the fewer emissions we emit. Improving fuel efficiency can be achieved through a combination of measures to improve the fuel efficiency of vehicles and decreasing the volume of fuel consumed through widening travel choices. This indicator tracks the fuel consumption per vehicle kilometre and per 1000 of population.
  • Proportion of new road vehicles that are alternatively fuelled: Improving the average efficiency of new vehicles is crucial to reducing emissions from the transport sector. Alternatively fuelled vehicles[15], including electric and hybrid vehicles, have the potential to emit very low levels of tailpipe emissions. This indicator tracks the proportion of vehicles newly registered that are alternatively fuelled.
  • Modal share of public transport and active travel: Promoting the use of public transport or active travel as an alternative to the private car is an important element of reducing transport emissions. This indicator tracks the proportion of average distance travelled per person per annum by public transport, walking or cycling.
  • Aviation passengers: Emissions from aviation have grown rapidly over the past 20 years. This indicator tracks the total number of aviation passengers, both terminal and transit.
  • Waterborne freight lifted in Scotland and moved: Commercial shipping constitutes the greatest element of maritime emissions. This indicator tracks the total level of waterborne freight lifted in Scotland and moved, measured in million tonne-kilometres.
Table 3: Trends in leading transport indicators[16]
Indicator 2010 level Average growth p.a. (2003-2010) Growth (2009-2010)
Road vehicle kilometres travelled (million vehicle kilometres) 43,488 +0.5% -1.7%
Proportion of new road vehicles that are alternatively fuelled (%) 0.6% +80% +71%
Modal share of public transport and active travel (distance travelled) (%) 20% 0% 0%
Aviation passengers (thousand passengers) 20,957 -0.1% -7%
Waterborne freight lifted in Scotland and moved (million tonne-kilometres) 15,722 -1% -12%
2009 level Average growth p.a. (2005-2009) Growth (2008-2009)
Road transport fuel consumption[17]
(a) tonnes per 1000 vehicle kilometres;
(b) tonnes per 1000 population.[18]

(a) 0.1
(b) 594

(a) -2%
(b) -0.3%.

(a) -3%
(b) -3%