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 construction of rolling stock, 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). 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 such as Transport for the North (TfN) or Network Rail, promoting new infrastructure, is that they will need to present a ‘whole-life’ approach which deals with all 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, there remains 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 rail based transport infrastructure to inform decision making. Some of the key findings of this analysis and general conclusions have been presented here.
Summary of Main Findings
- The whole life carbon (WLC) impacts of some planned developments/upgrades in the rail transport infrastructure (new tracks, bridges overhead line equipment (OLE) and station upgrades) were estimated employing life cycle assessment, over an assumed service life of 60 years.
- The whole life carbon of 1 km of track, modelled within the boundary constructs and the assumptions adopted in this study, is determined to be 2,024.3 tCO2eq for ballasted track and 1,662.2 tCO2eq for ballastless track.
- The whole life carbon (WLC) per unit of ballastless track is relatively low (-20%), while the overall energy intensity was observed to be about 2% higher, compared to that of the ballasted tracks.
- Resistance to vibrational impacts and lack of other moving parts means ballastless track needs little to no maintenance over the 60-year service life, saving 50% of operational emissions, relative to ballasted tracks.
- Track maintenance is the most material and energy intensive phase in the life cycle of a rail track, contributing 70% of the track’s whole life carbon.
- The main embodied carbon contributor for the tracks is the steel in the rails, clips and the rebar in the sleepers (58% of the embodied carbon of 1km track).
- OLE operation and maintenance are the most carbon intense phases and are responsible for 85% of its whole life carbon (electrified single track – 1,696 tCO2eq).
- The main embodied carbon contributor here again is the steel foundation (92% of the whole life carbon), followed by the conductor materials used in the catenaries of the OLE.
- Generally, carbon emissions related to energy demand peak during the ‘track operation and its maintenance’ over its life-period (2.8 GWh over 60 years).
Sensitivities to intersectoral interactions
- Use of low-carbon alternatives to the sleepers in new-rail-tracks reduces the whole life carbon by about 6-15% over the asset’s life period of 60 years.
- There is potential to extend these savings to 20-35% by integrating more recycled steel into the rails and for reinforcing concrete structures that are required to be replaced every 15-20 years.
- This study adopts two of the four grid decarbonisation pathways (Steady Progression and System Transformation) published by the National Grid in their ‘Future Energy Scenarios 2020’ report.
- A steadily decarbonising energy grid delivers whole life carbon savings for 1 km of an electrified rail track by about 12-23% under the ‘Steady Progression’ pathway, which is elevated to 25-64.5% under the ‘System Transformation’ pathway, relative to baseline figures estimated for the year 2020.
- The study assessed the use of solar PV modules of varying capacities (23-96 kWp) in stations of specific passenger capacity, over a service life of 60 years in the context of a steadily decarbonising grid.
- Carbon savings from the use of solar PV modules, that displaced grid-electricity, steadily decrease with time against the backdrop of a decarbonising grid.
- The solar PV modules are capable of paying-off their embodied carbon within one to two years of their installation (depending on the capacity installed and energy efficiency) and can therefore act as further mitigation against the embodied emissions from construction and maintenance. For some schemes this can be very significant although it is highly context specific.
- It is also possible that the carbon benefits of such installations are accounted for in the grid decarbonisation assumptions made in the FES study. Further investigation is required to explore whether PV can be used as further mitigation to carbon emissions from construction and maintenance.