Between 1989 and 2004, energy consumption for road freight in the UK is estimated to have increased by only 6.3%. Over the same period, UK GDP increased by 43.3%, implying that the aggregate energy intensity of UK road freight fell by 25.8%. During this period, therefore, the UK achieved relative but not absolute decoupling of road freight energy consumption from GDP. Other measures of road freight activity, such as tonnes lifted, tonnes moved, loaded distance travelled and total distance travelled also increased much slower than GDP. The main factor contributing to the observed decoupling was the declining value of manufactured goods relative to GDP. Reductions in the average payload weight, the amount of empty running and the fuel use per vehicle kilometre also appear to have made a contribution, while other factors have acted to increase aggregate energy intensity. The results demonstrate that the UK has been more successful than most EU countries in decoupling the environmental impacts of road freight transport from GDP. However, this is largely the unintended outcome of various economic trends rather than the deliberate result of policy.
The contribution of freight transport to climate change is substantial and growing. Globally, freight transport accounts for one third of transport energy consumption and around 8% of total energy-related carbon dioxide (CO2) emissions. The bulk of these emissions derive from heavy goods vehicles (HGVs), which in most countries account for the majority of freight activity. In the UK, for example, HGVs account for more than 68% of goods moved (tonne kilometres), 24% of road fuel use, 22% of transport CO2 emissions and 5% of total CO2 emissions (DfT, 2005b).
Despite this, freight transport has been relatively neglected in terms of both climate policy and the associated policy research. Policy initiatives to restrain the growth in energy use and carbon emissions from this sector (e.g. the UK Sustainable Distribution Strategy and Freight Best Practice programme) have been both limited and ineffective, while policy research has focused disproportionately upon passenger transport. Both the European Union and the UK have the stated goal of decoupling various measures of road freight activity from GDP, but this has generally been interpreted as relative rather than absolute decoupling – implying that energy use and carbon emissions could continue to increase, even if the objective was met.
Freight activity is driven by complex and interlinked trends in production, trade, distribution and retail, including income growth, wider sourcing of products, increased specialisation, ‘just-in-time’ distribution and increasing concentration of manufacturing and stockholding (Lehtonen, 2008, McKinnon and Woodburn, 1996 and NEI, 1997). The corresponding impact on energy use and carbon emissions may be either enhanced or offset by parallel trends in logistics, vehicle technology and the management of transport resources, including factors such as the size, fuel efficiency and average load factor of vehicles. Some of these trends have led to greater energy use in this sector over recent years, while others have encouraged reductions in energy use. If the growth in carbon emissions from freight transport is to be halted and reversed, the nature and relative importance of these trends needs to be better understood.
This paper contributes to that end by examining trends in ten variables that have strongly influenced UK road freight energy consumption over the period 1989–2004. Following McKinnon (2007), we call these variables key ratios since they are each formed from the ratio of two other variables which we term key quantities. For example, the ratio of the ‘goods moved’ by freight vehicles (tonne kilometres) to the ‘goods lifted’ by freight vehicles (tonnes lifted) represents one such key ratio (the average ‘length of haul’).
This paper shows how UK road freight energy consumption can be expressed as the product of these ten key ratios and GDP. Some of these key ratios (e.g. the average length of haul) have increased in magnitude since 1989 and thereby led to greater energy consumption, while others (e.g. the amount of empty running) have decreased and led to reduced energy consumption. The paper explores the measurement, meaning and significance of these key ratios, together with the key quantities from which they are formed, and summarises their trends over the period 1989–2004. It also examines how these trends vary between different vehicle types and commodity groups. The analysis is much more disaggregated than previous studies in this area (e.g. Kamakaté and Schipper, 2009) and provides a nuanced picture of the factors underlying the aggregate trend in UK road freight fuel consumption. This in turn allows the main reasons for the observed decoupling to be identified.
