Chapter 2: Historical emissions analysis
2.1 Background and data sources
The emissions data presented in this chapter are from the 'Greenhouse Gas Inventory for England, Scotland, Wales and Northern Ireland: 1990-2011'10 (GHGI) unless otherwise stated. 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)11.
The transport category within the GHGI covers emissions from road, aviation, rail and maritime transport. While domestic aviation and shipping emissions are recorded in the GHGI, emissions associated with international aviation and shipping (IAS) were not originally reported. 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 IAS 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.
In line with the methodology used to report against the Climate Change (Scotland) Act, the transport emissions reported in this section 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.
Greenhouse gas emissions for European Union Member States are reported in the 'European Union greenhouse gas inventory 1990-2011 and inventory report 2013'. This is compiled on an annual basis by the European Environment Agency and includes aggregate data for all member countries of the EU12. Data from other Member States has been included in the CAT for the first time for the purpose of comparing relative performance across countries.
2.2. Total emissions trends for Scotland and the Scottish transport sector
In 2011 total Scottish emissions from all sectors amounted to 51.3 mega-tonnes of carbon dioxide equivalent (MtCO2e)13. This total represents a 5.6 MtCO2e or 9.9% fall from the equivalent 2010 figure. Compared to the 1990 base year Scotland has reduced its total emissions by 29.6%.
Transport's share of this Scottish total is 13.0 MtCO2e. After an initial sequence of almost continual increases in emissions from 1990, the run peaked in 2007. Since reaching this peak of 14.7 MtCO2e transport emissions have fallen year on year and are now back to their 1990 base year level, 12% or 1.7 MtCO2e below their 2007 peak.
The recent falls in emissions has been as a result of a number of factors. Principal among them are the wider economic conditions and stagnating real household incomes, but factors such as investment in public transport infrastructure, improvements in fuel efficiency, government environmental policies, land-use planning and global oil prices will also have played a significant role.
The latest data on economic performance in Scotland shows a number of quarters of positive GDP growth. The close correlation between GDP and transport emissions suggests that this will put pressure on the continuation of the recent trend of reducing emissions.
With IAS emissions excluded, the transport sector accounts for 20.4% of total Scottish emissions. With them included this figure rises to 25.3%. The respective shares in 2010 were 18.8% and 23% and 14.4% and 17.7% back in 1990. Figure 1 shows the growing relative importance of transport emissions in Scotland.
Figure 1: Total emissions from transport and transport emissions as a percentage of total Scottish emissions, 1990-2011
Source: Greenhouse Gas Inventory, NAEI, 2013, Transport Scotland. Total emissions calculation excludes the impact of the EU Emissions Trading System.
2.3 Emissions analysis by transport sector
2.3.1 Road Transport
Road transport emissions include all private, public and commercial road vehicles. In total, this category accounts for 71.5% of total transport emissions. In 2011 total road emissions fell to 9.3 MtCO2e - a fall of 1.7% against the equivalent 2010 figure. Although total road emissions declined, Light Good Vehicles (LGVs) emissions increased by 1% in 2011, and overall LGV emissions show an increase of 71% since the 1990 base year.
Figure 2 shows that road emission rose almost continuously from 1990 to a peak in 2007 of 10.2 MtCO2e. Since this 2007 peak, road emissions have fallen for four years and in 2011 stand 9.2% below this peak. Road emissions are though still 1.8% above the 1990 equivalent figure.
Figure 2: Road transport emissions 1990-2011 and road transport emissions as a share of total transport emissions
As well as reflecting improvements in car energy efficiency, road transport emissions have been affected by changes in the make-up of the passenger car fleet. With diesel engines being more fuel efficient than their petrol equivalent (all other things being equal) the balance of the fleet moving in favour of diesel (see Figure 3) has improved the emissions situation. Further detailed analysis of road transport emissions by vehicle type and road type is undertaken in sections 2.4 and 2.5.
Figure 3: Distribution of new Scottish registrations between petrol and diesel 1999-2011 - all vehicle body types
2.3.2 Maritime Transport
Emissions from maritime transport14 in 2011 are estimated to be 1.8 MtCO2e or 14% of total transport emissions. Figure 4 shows that emissions from this sector have been volatile, although this is due in part to methodological and GHG reporting changes.
Maritime emissions fell by over one million tonnes from their 1998 peak of around 2.8 MtCO2e to 1.7 MtCO2e in 2002. Thereafter they rose by 0.6 MtCO2e to reach 2.3 MtCO2e in 2008 before subsequently returning to near their 2002 low. The 2011 estimate is 31% or 0.8 MtCO2e below the equivalent 1990 figure. The volatility in the series can be attributed to the performance of international shipping sector (IS) as historically IS emissions account for more than 70% of all maritime emissions. Figure 5 also shows domestic maritime emissions are on a gentle downward pathway.
Figure 4: Maritime transport emissions and maritime transport emissions as a share of total transport emissions
Figure 5: Comparison between domestic and international shipping emissions
In 2011 aviation emissions increased by 3.4% over their 2010 level to 1.7 MtCO2e, some 0.6 MtCO2e or 52% above the 1990 base year. Aviation emissions now represent 13% of total transport emissions. Figure 6 shows the increasing trend in emissions from 1990 out to 2007 (2.2 MtCO2e) before decreasing to 1.6 MtCO2e in 2010 - a level last recorded in 2003.
Figure 6: Aviation transport emissions and aviation transport emissions as a share of total transport emissions
Figure 7 shows that from 1998 to 2003 emissions from domestic and international aviation were very similar. Since then the series have diverged. In 2011 international aviation emissions are estimated to account for 62% of total Scottish aviation emissions, almost the opposite of the situation in 1990 when domestic aviation emissions accounted for almost two-thirds of aviation's total. Between 2010 and 2011 domestic aviation emissions are estimated to have continued to decline (by 3.4%) while the emissions from international aviation rose by 8.1%.
Figure 7: Comparison between domestic and international aviation emissions
2.3.4 International Aviation and Shipping
After peaking in 2006 at 3.0 MtCO2e, emissions from IAS were almost 0.6 MtCO2e lower in 2010 at 2.4 MtCO2e. The 2011 estimate shows an increase of 8.1% for International Aviation (IA) and a 0.9% increase for International Shipping (IS) increasing the aggregate IAS total to just under 2.5 MtCO2e. Between 2007 and 2010 the number of international flights from Scotland fell by 13.9% and emissions form international aviation fell by 21.4%. International flight departures rose by 8.9% between 2010 and 2011 and IA emissions increased by 8.1% over the same period.
The estimates for IS emissions rose marginally in 2011 but remain at 1.4 MtCO2e. This is the first increase in the estimate for IS since 2006 although the current estimates are still significantly below those before 2000. Overall, the emissions estimate for 2011 is the same as for the base year although the split in emissions between the two has changed from 4:1 shipping to aviation to 3:2 in favour of shipping over aviation.
Figure 8: International maritime and aviation emissions 1990-2011
Rail emissions rose by 3.4% between 2010 and 2011 and the 2011 emissions total of 0.2 MtCO2e is 43% above the equivalent 1990 figure. Rail emissions show the steadiest increase over time but still only account for 1.4% of all transport emissions in Scotland. Total passenger kilometres travelled by rail have increased by over 34% for the period 2003-04 to 2012-15 and scheduled train kilometres have increased by over 19% over the same period.
Figure 9: Rail transport emissions and rail transport emissions as a share of total transport emissions
2.4 Road emissions by vehicle type16
Emissions from cars have fallen from a peak of 6.0 MtCO2e in 2002 to an estimated 5.2 MtCO2e in 2011, a fall of around 14%. Over the same period (2002-2011) car kilometres have risen from 33.2 billion kms to 33.6 billion kms. Compared to the 1990 base year car emissions have fallen by around 0.6 MtCO2e or 10%. Despite this fall, car emissions continue to account for the greatest proportion of road transport emissions at 56%, and 40% of all transport emissions.
2.4.2 Heavy Goods Vehicles
HGV emissions make up the second largest proportion of road emissions and are estimated at 2.1 MtCO2e in 2011. HGV emissions fell slowly between 1990 and 2002 before growing rapidly. By 2006 HGV emissions surpassed their 1990 baseline figure of 2.1 MtCO2e reaching 2.2 MtCO2e in 2007. Emissions fell marginally in 2011 compared to 2010 but at 2.1 MtCO2e are still 2% above their 1990 level.
2.4.3 Light Goods Vehicles
There has been a 71% increase in LGV emissions since 1990. Emissions also increased by 1% between 2010 and 2011. At 1.4 MtCO2e in 2011 they account for 15% of road emissions and 10% of total transport emissions.
2.4.4 Other - Buses and Motorcycles
Emissions from buses fell by 6.3% between 2010 and 2011 and now account for 0.5 MtCO2e. Current bus emissions are though still 0.1 MtCO2e or 36% above the 1990 base year emissions estimate of less than 0.4 MtCO2e. After rising in 2011-12 passenger boardings fell back in 2012-13.
Motorcycle emissions rose by 1% compared to 2010 but remain at 0.03 MtCO2e and account for just 0.4% of road emissions and 0.3% of total transport emissions.
Figures 10, 11 and 12 illustrate the changes in road emissions by vehicle type, the share of each vehicle type in total road emissions and the year in year change in car, HGV and LGV emissions respectively.
Figure 10: Breakdown of road emissions by vehicle type 1990-2011
Figure 10 shows that goods vehicles were largely responsible for the increase in road emissions to 2007. Since then the decline in emissions from car has been behind the overall reduction in road emissions. The change in shares between vehicle types between 1990 and 2011 can be seen in Figure 11.
Figure 12 shows five consecutive year-on-year falls in car emissions from 2006. The pattern with goods vehicles is more mixed with 2008 and 2009 being the only years in which there was a reduction in emissions for both goods vehicle types.
Figure 11: Share of road emissions by vehicle type in 1990 and 2011
Figure 12: Year in year change in car, HGV and LGV emissions 1995-2011
2.5 Road emissions by road type
Emissions on rural roads have fallen for four consecutive years since 2007. In 2011 rural road emissions are estimated at 4.7 MtCO2e, 0.1 MtCO2e or 2% below the 2010 figure. The latest year's estimate is just below the base year figure of 4.8 MtCO2e. Rural emissions account for just over half of total road emissions.
2011 urban emissions are 7% below their 1990 level at an estimated 3.0 MtCO2e, down from a peak of 3.2 MtCO2e in 2007. Emissions from urban traffic currently account for 31% of road emissions.
Emissions from motorway traffic account for the smallest proportion in road emissions at just 19%. At 1.7 MtCO2e they are only marginally greater than the 2010 estimate, rising by just 0.1%. However the share in emissions from motorway traffic has been growing and shows a 41% increase over the share in 1990.
Figure 13: Emissions by road type (Index=1990 for each road type)
Figure 14: Share of road emissions by road type
2.6 Comparison of key Scottish and UK transport emission statistics
Table 1 sets out a number of comparisons between UK and Scottish emissions by broad sector or category, and over short term and longer term timescales.
Table 1: Comparison of Scottish and UK GHG emissions
||Scottish emissions as a % of UK emissions
||Change in Scottish emissions
||Change in UK emissions
||Change in Scottish emissions
||Change in UK emissions
|All Transport (excl. IAS)
|Aviation Transport (incl. IA)
|Maritime Transport (incl. IS)
- In 2011 Scottish transport emissions, including IAS, accounted for an estimated 8.1% of total UK transport emissions and 8.9% of emissions if IAS is excluded.
- The share of emissions from buses, traffic on rural roads, domestic and international maritime combined and from domestic aviation are disproportionately greater in Scotland than in the UK as a whole, with the opposite holding true for motorway emissions and aviation including international aviation emissions. The shares in other categories are broadly similar to the overall picture.
- Between the 1990 base year and 2011 transport emissions in Scotland have risen by 0.1% whereas for the UK as a whole the rise is 10.5%. Without the inclusion of IAS the change for the UK as a whole (-2.5%) is greater than for Scotland (-0.2%)
- Between 2010 and 2011 the fall in Scotland's transport emissions, with or without IAS included, outperformed the UK as a whole.
- Over time, all sub-categories of Scottish transport emissions have tended to change broadly in line with the equivalent UK series.
- Rail emissions in Scotland have increased significantly since 1990 albeit from a very small absolute base figure. In 2011 Scottish emissions are 42.6% above the 1990 equivalent accounting for 8.4% of UK emissions. The overall rail emissions in the UK rose by 7% between 1990 and 2011.
- Scottish aviation emissions (with IA included) account for only 4.6% of the total UK aviation emissions but this percentage rises to 16.3% if only domestic aviation emissions are considered. This is to be expected given the relative importance of international aviation traffic (and emissions) in England relative to Scotland.
- Emissions from maritime transport in Scotland fell by 1.8% between 2010 and 2011 whereas the UK equivalent percentage rose by 7.4% for the same period. Although maritime emissions in Scotland and in the UK are well below the 1990 figure (36.1% and 11.4% respectively), if IS is included UK emissions are by 3.9% above the 1990 level while Scotland's emissions are over 30% lower.
Breaking down the UK estimates to the four home countries sheds a little more light on Scotland's performance relative to England, Wales and Northern Ireland.
Table 2: Comparison of Scottish, English Welsh and Northern Irish GHG emissions 1990 - 2011 and 2010 - 2011
||Maritime (incl. IS)
||All Transport (incl. IAS)
|Change in emissions
|Change in emissions
|Change in emissions
|Change in emissions
- Compared with the 1990 base year, the Scottish aggregate emissions total (incl. IAS) shows only a 0.1% increase whereas the increases in England, Wales and N. Ireland are 11.6%, 1.7% and 28.1% respectively. Excluding IAS the performance of both England and Wales over the same period is better than in Scotland, and it is the same outcome considering road emissions alone.
- Scottish emissions reductions in 2011 exceed those from any other country of the UK, including or excluding IAS. All transport emissions reduced by 2.1% compared to 1.3%, 1.8% and 1% in England, Wales and N. Ireland respectively. If International Aviation and Shipping is included Scotland is the only country to reduce its emissions in 2011.
2.7 Comparison of key Scottish and Nordic transport emission statistics
Considering Scotland's geographic climatic and demographic similarities with the Nordic States a comparison between the transport emission figures is provided below. The trends in transport emissions are taken from Eurostat and cover road, rail, inland navigation and domestic aviation.
Scotland is the only country whose longer term performance shows an emissions decrease compared to 1990 and while its performance in the latest year on year comparison is not as good as Sweden or Denmark it still shows a significant reduction.
Table 3: Comparison of total and percentage change in Scottish and Nordic States GHG emissions KtCO2e 1990-201117
||Base Year 1990
||% change 2010-2011
||% change 1990-2011
Source: European Environment Agency (EEA, Greenhouse Gas Emissions from Transport 2013, http://epp.eurostat.ec.europa.eu/tgm/table.do?tab=table&init=1&plugin=1&language=en&pcode=tsdtr410
Figure 15: Comparison of transport emissions (excl. International Aviation and Shipping) in Scotland and the Nordic Countries
Figure 15 shows that all countries exhibited an increasing trend in transport emissions between 2000 and 2007. However, the increase in Scottish emissions over the period was lower and since 2007 there has been a consistent year on year reduction in Scotland unlike in Finland, Sweden and Norway.
2.8 Comparison of key Scottish and EU transport emission statistics
A further useful performance comparison is with EU member states. Table 4 shows that only three countries, Germany, Estonia and Lithuania have actually reduced their transport emissions comparing 2011 with their 1990 equivalent figure. Scotland has also seen a small emissions reduction based on the definition used in this EU estimate. Many of the other member states show a substantial increase in emissions over the period with 5 having increases of over 100%. The UK outcome is unchanged from its 1990 equivalent figure.
Table 4: Transport emissions in Scotland compare to transport emissions of EU- member states18
||% change 1990-2011
||% change 1990 -2011
||EU (27 countries)
2.9 Efficiency of passenger vehicles
By measuring the efficiency of passenger vehicles in terms of the CO2e per passenger kilometre (ppkm)19 another useful picture for transport emissions emerges to help consider ways to reduce aggregate emissions. According to Defra's Company Reporting Guidelines20 an average coach generates just under 30g CO2e/ppkm, rail just under 50g CO2e/ppkm and bus 112g CO2e/ppkm. The average petrol car produces emissions of 129g CO2e/ppkm. Since 1999 average car occupancy has fallen by 9.5% acting as a drag on the improved efficiency of the internal combustion engine. Domestic flights are estimated to be the most polluting per passenger kilometre followed by petrol cars, international long haul and diesel cars.
Table 5: CO2e emissions per passenger kilometre by mode21
||Average petrol car
|Average diesel car
|Average petrol hybrid car
|Average petrol motorbike
|Light rail and tram
|Ferry (Large RoPax)
||Average foot and car passengers
||Average domestic flights
|Average short haul international
|Average long haul international
Source: 2013 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting, http://www.ukconversionfactorscarbonsmart.co.uk/
2.10 Leading indicators
Data on greenhouse gas emissions emerges around 18 months after the end of the year in question. Unfortunately, there are not a huge number of readily available lead indicators, but those available are discussed below and reported in Table 6.
- Road vehicle kilometres travelled: Road emissions are directly related to the kilometres travelled. This indicator tracks vehicle kilometres travelled by all vehicle types on all roads. Since 2007 the trend in total kilometres travelled in Scotland has been a slow decline to 2011, although in 2012 total road kilometres travelled increased marginally.
- Proportion of new road vehicles that are alternatively fuelled: Alternatively fuelled vehicles, including electric and hybrid vehicles, produce fewer GHG emissions per kilometre. An increase in the proportion of those vehicles on the road will reduce emissions from the transport sector. This indicator tracks the proportion of vehicles newly registered that are alternatively fuelled. The latest data shows that there was a small decrease in the proportion of alternatively fuelled vehicle sold in 2012 (although actual sales increased).
- 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. The latest available survey data suggests a continued slow modal shift towards sustainable and active travel.
- Aviation passengers: Emissions from international aviation in particular have grown rapidly over the past 20 years. This indicator tracks the total number of aviation passenger - both terminal and transit - and shows another small pick-up in passenger numbers between 2011 and 2012. The number of aircraft movements at Scottish airports also increased.
- 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. The latest estimate to 2012 shows a further decline in million-tonne kilometres and the figure is now at its lowest level for well over a decade.
- 2012 UK emissions estimates: Final UK emissions data for 2012 was published in February 2014 while final Scottish data for 2012 will not be published until June. The latest UK transport emissions estimate shows a small reduction in emissions of less than 1% in 2012 compared to 2011, continuing the downward trend begun after 2007. While not part of the headline UK calculation, the estimate of UK emissions from IAS also fell in 2012 compared to 2011. Even though there tends to be a strong correlation between movements at the UK and Scottish levels there is no guarantee that this fall for the UK as a whole will be replicated in Scotland.
- Road transport fuel consumption per vehicle kilometre: Vehicle fuel efficiency is a key element in emissions reduction. By reducing fuel consumption per vehicle kilometre fewer emissions are emitted. This indicator tracks fuel consumption per vehicle kilometre and per 1000 population and shows a continuing improvement in both indicators.
Together, the available indicators suggest that downward pressure will continue to be felt on transport emissions in the short term although the small pick-up in airline passenger numbers and kilometres travelled by road will dampen that downward pressure.
Table 6: Trends in leading transport indicators22
||Average growth p.a. (2003-2012)
|Road vehicle kilometres travelled (million vehicle kilometres)
|Proportion of new road vehicles that are alternatively fuelled (%)23
|Modal share of public transport and active travel (distance travelled) (%)24
|Aviation passengers (thousand passengers)
|Waterborne freight lifted in Scotland and moved (million tonne-kilometres)
|UK transport emissions (excl. IAS) (MtCO2e)
|UK petroleum consumption by transport (million tonnes)
|GB Average new car fuel efficiency:
||Average growth p.a. (2005-2011)
|Road transport fuel consumption25
Kilogrammes per 1000 vehicle kilometres;
|Kilogrammes per 1000 population.26
On the Move: car, rail and bus travel trends in Scotland
In June 2013 Transport Scotland published: On the Move: car, rail and bus travel trends in Scotland, a follow on to a similar GB wide study. While the first study used the National Travel Survey data collected across GB as a whole and thus has a small Scottish sample, this second study considered Scotland alone, using Scottish Household Survey data for its analysis. Scottish Household Survey data was available for the period up to and including 2008/10)
One of the main objectives of this two studies was to consider trends in car, bus and rail travel from the mid-1990's onwards, and within this to further ask whether individuals were showing signs of experiencing 'peak car' - a sustained period of flat or even downward trending levels of car use per person.
Both studies showed basically flat trends car use per period over the data period but neither could be shown to be statistically significant. For example the National Travel Survey shows that average annual car driving mileage per person rose by 3% but this increase is not statistically significant due to the small sample size. Traffic count data for both shows a slow steady growth in car traffic up to 2008 (2008/10 was the latest dataset available) and a gradual lengthening of journey distance.
While men's driving distances have been falling, women's have been increasing due primarily to more women driving. Young men's driving mileage has trended downwards more sharply than any other demographic group, but there is no evidence that they have been switching modes. Fewer of this demographic group hold licences while licence-holding for older groups has been increasing, particularly for women.
Bus use per person has grown slowly over the period and seems to be caused by more intense service use rather than use by new patrons. As with car journeys length of bus journey has been increasing but use of bus for commuting has been falling. Bus travel has risen most markedly amongst men aged 60 and over.
Rail use per person has grown driven mainly by more people using rail. There is some evidence to suggest Scottish residents are making longer distance journeys which is corroborated by a significant growth in cross-border ticket sales. Commuting by rail has increased over the period, and rail trips are, unsurprisingly on average several times longer than either car or bus journeys.