skip to content | Accessibility Information

High Speed Rail


Transport, especially high speed, is critical for both economic and social development. In response to mounting environmental concerns, particularly in relation to climate change, the UK Government is seeking to identify the most sustainable transport options for the UK transport network. Key factors for comparison include carbon dioxide (CO2) emissions, capacity, demand and the carbon implications of existing and new infrastructure and technology. These factors will vary on different city pair routes, therefore comparisons need to be made in order to identify the most suitable mode for each journey.

Aims and Objectives:

To comparatively analyse by a life cycle assessment (LCA) the carbon implications of air and rail transport options for satisfying future high speed transport demand in the UK.

  1. To establish the role of air and rail transport within the UK, examine existing UK transport policy and critically assess its compatibility with the UK’s commitment to carbon reduction and sustainable mobility;
  2. To identify the inherent carbon efficiency associated with meeting the present demand for domestic air and rail transport between key city pairs within the UK by a LCA;
  3. To examine the anticipated and potential technological and operational developments for future air and rail transport;
  4. To quantify and compare, by a LCA, the CO2 consequences associated with meeting future demand for high speed transport between key city pairs in the UK, considering potential infrastructure, technology and operational developments, as well as load factors;
  5. To develop a policy support toolkit based on recommendations emerging from the LCA to assist decision makers in developing appropriate infrastructure for a sustainable high speed transport network within the UK. 


The UK Committee on Climate Change (2009) have acknowledged that growth in aviation, without improvements in technology and operations, will increase emissions further in this industry, making carbon reduction targets harder to achieve. The Committee’s 2009 report ‘Meeting the UK aviation target – options for reducing emissions to 2050’ made assumptions on future technological development, the uptake of alternative fuels and improved air traffic management and stated that a growth of only 60% in UK air transport could be accommodated for if CO2 emissions in the industry are not to exceed 2005 levels by 2050, a target the UK Government has set.

In order to curb passenger growth and CO2 emissions from UK domestic aviation, the Government are concentrating on a modal shift from air to rail. In March 2010, the Government unveiled plans for a new high speed rail line running initially from London to Birmingham, with possible expansion to the North of England and Scotland (see figure 1). The plans published by a new company, High Speed Two (2010), expect work on the construction to begin in 2015. However, a detailed comparison of the true CO2 intensity of high speed rail transport in the UK has not been established. Previous analysis has concentrated on emissions from operations, ignoring the CO2 intensity of construction and maintenance. Yet a recent study in North America stated that emissions from non-operational activities (such as maintenance and track construction) could be almost double that of operational emissions for rail transport over its entire working life (Chester and Horvath, 2009). With a legally binding climate change target agreed in 2008 to reduce greenhouse gas emissions by 80% (from a 1990 baseline) by 2050, any new transport developments need to have minimal carbon impacts. Table 1 highlights the carbon reduction targets (budgets) set under the 2008 Climate Change Act.

Figure 1. Proposed High Speed Rail Route (High Speed Two, 2010)

Budget Time Period Carbon Reduction Target (from a 1990 baseline)
1 2008 – 2012 22%
2 2013 – 2017 28%
3 2018 – 2022 34%
4 2023 – 2027 50%
Ultimate target of 80% reduction (from a 1990 baseline) by 2050

Table 1. 2008 Climate Change Act Carbon Budgets (DEFRA, 2008)

This research has established the need for a detailed life cycle assessment (LCA) of rail and air transport, taking into account key variables that will determine future CO2 emissions (these include construction, technological changes, and load factors as a result of modal shift).



A life cycle approach has been taken and applied to the chosen city pair routes in the UK, this technique allows for a detailed comparison of a number of different elements which may contribute to significant CO2 emissions throughout the course of the journey for air and rail transport. The results of this will establish which modes are most effective for which journey (in terms of carbon intensity) and also what the ideal scenario may be for the future high speed transport options in terms of meeting the climate change goals and establishing a sustainable high speed transport network. These results will establish whether investing in high speed rail is the right way forward in terms of reducing CO2 emissions in the transport sector, or whether concentrating on other developments would be more beneficial.


Baseline Models: Air and rail transport in the current situation will be analysed on their inherent CO2 output (kg CO2 per available passenger kilometre (apk), this identifies areas of current significant CO2 output. Creating these baseline models allows for future developments to be analysed against the current situation.


Future Models: Future options for air, conventional rail and high speed rail will be analysed by LCA on their apk CO2 output.

  • High, medium and low scenarios will be established for future options
  • Future air transport data comes from Committee on Climate Change 2009 report, which establishes high, medium and low future scenarios for developments in technology and improvements in operations
  • Conventional rail:
    • Detailed breakdown of future electricity generation
    • Improvements in current rolling stock
  • High speed rail:
    • Range of assumptions on energy consumption
    • Construction emissions

The outcome of this analysis will be to identify the most efficient future transport scenario (in terms of reducing CO2 output) for each studied route.

Load Factor Analysis: Once the inherent CO2 outputs for future options in air and rail transport have been identified, an analysis of their performance at varying load factors then needs to be carried out. This analysis allows for recommendations of passenger numbers to be made, in order for a particular mode or technology to be operating efficiently. Several load factor scenarios have been established;

  • Current load factors (actual load factors)
  • Predictions in future load factors (a range of assumptions from various sources)
  • Hypothetical scenarios for finding ‘tipping points’ for efficiencies (e.g. at which point does a transport option become inefficient because they are operating at a too low load factor? What load factor is needed for a transport option to be operating efficiently?)

The recommendations from the LCA will highlight the optimal transport modes and developments, in terms of lowering CO2 emissions, for each city pair route analysed. Findings from the load factor analysis will recommend the passenger numbers needed in order to make a particular mode or development efficient in terms of reducing CO2 emissions in line with the Climate Change Act target. Ultimately these findings will assist in the decision making for future transport developments in the UK and in the goal of incorporating high speed transport into a sustainable transport system that meets the needs of the UK population without compromising the targets set under the 2008 Climate Change Act.

Key Outcome:

This project will contribute to understanding the environmental impacts of air and rail options for high speed transport in the UK, taking into account direct and indirect processes (construction, operation, and infrastructure) of future developments and identify the most practical solution in terms of meeting the UK’s targets for carbon reduction. It will have a lasting impact through providing a strategic toolkit for policy makers.