Executive Summary

The Department for Transport’s Decarbonisation Plan focuses on ‘tailpipe emissions’ from vehicles. Whilst the plan acknowledges embodied emissions in the construction and management of infrastructure and the building of new vehicles, no clear indications of the scale of these emissions nor their significance have been provided. The national accounting responsibility for those embodied emissions sits with the Department for Business, Energy and Industrial Strategy (BEIS) at a national scale. So, the Department responsible for generating these emissions through decisions to expand infrastructure (DfT) is not responsible for managing those emissions. The reality for organisations promoting new infrastructure, such as Transport for the North (TfN), is that they will need to present a ‘whole-life’ approach which deals with all of the carbon implications of their choices.

Shifting to a ‘whole-life’ carbon (WLC) approach requires an understanding and assessment of embodied carbon at the ‘design’ stage to become a part of strategic decision making, leading to investment programmes compatible with climate commitments. However, perhaps because of the lack of focus on these issues within DfT and the lack of responsibility for transport infrastructure within BEIS, the departments currently offer limited guidance, expertise and experience in understanding how important embodied emissions might be to different types of investment cases.

The aim of this work is to quantify the embodied and operational carbon associated with the systems and sub-systems in the roads transport infrastructure to inform decision-making.

Summary of Main Findings

The whole life carbon (WLC) impacts of some of the key components of the road transport infrastructure (construction of a new road, lighting operation and maintenance of the built asset) were estimated employing life cycle assessment, over an assumed service life of 40 years. Please see S_Figure 1.

Road report graph
S_Figure 1: Life cycle carbon emissions associated with different scales of asphalt pavement construction
  • The whole life carbon of 1 km of road, modelled within the boundary constructs and the assumptions adopted in this study is determined to be 2,658.9 tCO2eq for dual-3 lane; 2,014.1 tCO2eq for dual-2 lane; and 880.3 tCO2eq for single-2 lane carriageway.
  • The ‘Material production’ phase is determined to be the dominant carbon contributor across the whole life of a road.
  • The key embodied carbon contributors are the energy-intensive materials, concrete and asphalt.
  • The surface layer of the asphalt pavement (road) is the most energy intense (5 TJ over the asset’s assumed service life of 40 years), followed by the embodied energy of the sub-grade layer (4.2 TJ).
  • Material-related emissions are closely followed by those attributed to material transport energy needs and thus electricity production and supply. Road-lighting operation is the next highest carbon contributing sub-system in the whole life cycle of a new road, responsible for 12-15% of the asset’s whole life carbon. 

Sensitivities to inter-sectoral interactions

  • Use of low-carbon alternatives and secondary (reclaimed) materials could reduce the whole life carbon of new roads by 2-12% over the asset’s life period of 40 years (2020-2060).
  • A decarbonising energy grid could reduce the whole life carbon of new roads by 8-42% over the asset’s life period between 2030 and 2060, relative to the 2020 estimates. The level of savings is dependent on the certainty to which the grid decarbonisation occurs, including the technological integration, maturity and the level of societal behavioural change assumed within the FES 2020 scenarios.
  • In the assessment of a hypothetical scenario, in which an optimistic grid decarbonisation pathway (System Transformation) is applied across the whole life of the built assets, with access to negative carbon (‘CCS’ setting), 10-30% of whole life carbon remains a challenge to achieving carbon neutrality even in the long-run. One of the main contributors of this ‘stubborn’ remainder of whole life carbon is the embodied carbon in the materials.
A breakdown of the systems and sub-systems embedded in an asphalt pavement, representing the system boundary of this study (Dashed lines show those sub-systems and processes that are within the scope of study)

Read or download related reports:

Policy Briefing: Everything Counts

Measuring Railway Infrastructure Carbon