In a transport context the term embodied carbon refers to carbon dioxide emitted at all stages of the construction process. There is a small but increasing evidence base for the incorporation of embodied carbon into transport appraisal. At this stage Transport Scotland will pursue a methodology based on the existing data available. The approach and values will be updated and refined as the evidence base matures.
The recommended values are shown below. Values for maintenance are not currently available.
Rail
|
Category |
Tonnes CO2 |
| Track | 500 per single track km |
| Electric infrastructure | 450 per single track km |
| Stations | 100 per standard station structure |
| Bridges | 2,500 per standard bridge structure |
Road
|
Category |
Tonnes CO2 |
| Major road | 325 per lane km |
| Urban minor road | 300 per lane km |
| Rural minor road | 225 per lane km |
| Lighting (trunk) | 20 per annum, per lane km |
| Bridges | 2,500 per lane km |
Optimism bias and embodied carbon
Insofar as optimism bias uplifts reflect increases in capital cost above construction price inflation, assuming that cost is directly correlated to quantity suggests that it would be appropriate to apply optimism bias uplifts to these emissions.
Valuation of carbon emissions
Assuming that most transport projects will now be built post-2012, these emissions will occur within the traded sector (covered by the EU Emissions Trading System (ETS)), and therefore will be included in the capital cost of the project, as firms will have to buy permits to emit the associated carbon. Therefore, the emissions should be included in the overall calculation of carbon emissions but not valued within the appraisal.
There will be additional emissions associated with construction that will be outside the traded sector, and should currently be measured and valued in the standard way using the Shadow Price of Carbon (see section 7.4.2.6). Evidence on the scale of these impacts is limited, so a 20% uplift to the base values is recommended.
