Baseline emissions

Operation, maintenance, and improvement of the TRN have net emissions of 110 ktCO₂e per year. That is the equivalent of driving the length of Scotland over 1,700 times in a small diesel car and equates to around 31 tCO₂e per km of road.

Of the three activity areas, maintenance is the largest source of emissions, accounting for 81% of the total. Improvement activities contribute 10%, while operation accounts for the remaining 9%. Operational emissions are partially offset by carbon sequestration from land owned by Transport Scotland, excluding any tree planting undertaken for corporate offsetting purposes.

Figure 1 shows overall emissions are dominated by materials, which account for approximately 77% of total net emissions (or 71% excluding land sequestration). These are primarily embodied emissions generated during the extraction, processing, and manufacture of construction materials.

Figure 1 – Graph showing total annual emissions of TRN (ktCO2e) presented by emission source, as described in text before
Figure 1 – Graph showing total annual emissions of TRN (ktCO2e) presented by emission source

Operation

Includes regular inspections, cleaning, grass-cutting and routine maintenance activities, as well as the running of depots and vehicles, and the energy consumed by lighting signage on the network. Lighting is an important emission source in our operation of the TRN and so is included in our baseline emissions, although it is already officially reported to Scottish Government as part of our corporate accounting. Operation emissions also include emissions and removals from the atmosphere from Transport Scotland owned land.

Maintenance

Activities are individual and non-routine. Examples include resurfacing and reconstruction, maintenance and replacement of kerbs and fences, works to bridges, earthworks and drainage.

Improvement

Activities go beyond maintaining existing assets, to provide enhancement, for example works to adapt the TRN to a changing climate.

Business as Usual

Without any further decarbonisation interventions, it was estimated that emissions would decrease by 6% by 2045 due to background decarbonisation of the UK electricity grid. That is not sufficient to support Scottish Government in achieving its Net Zero commitments and it is clear that action is required.

Maintenance & Improvement

As shown in Figure 2, maintenance and improvement activities have very similar emissions profiles and are characterised by a high proportion of embodied carbon. Materials account for more than 80% of emissions in this category.

Asphalt is the single largest contributor, reflecting the volumes used and its carbon intensive production process. Thermoplastic road marking materials are the next largest source. Transport of materials to site contributes approximately 14% of emissions, while waste management accounts for less than 4%. Improvement activities have a higher contribution from steel, reflecting the nature of enhancement works.

Figure 2 – Diagram showing Maintenance & Improvement emissions (ktCO2e), as described in text before
Figure 2 – Diagram showing Maintenance & Improvement emissions (ktCO2e)

Operation

Figure 3 shows operational emissions are primarily associated with energy use, with the largest contributions coming from electricity and white diesel.

Electricity powers our Operating Company depots, but also our roadside electrical assets such as streetlighting and signage. This latter use accounts for over 92% of our electricity use.

Red diesel and gas oil used for plant and generators accounts for 12% of our operation emissions. This is fuel for the plant and generators used in maintenance and improvement activities.

Waste management accounts for 8% of our operation emissions. The majority of waste is recycled with minimal waste going to landfill.

Figure 3 – Diagram showing Operation emissions (ktCO₂e), as described in text before
Figure 3 – Diagram showing Operation emissions (ktCO₂e)

Figure 4 shows the embodied emissions of asphalt contribute almost half of total material emissions. Thermoplastic screed used in road markings also contributes a large number of emissions. Remaining emissions arise from a wide range of materials used in smaller quantities, including metals, resins, and timber.

Figure 4 – Diagram showing Material embodied emissions (ktCO₂e) presented by material, as described in text before
Figure 4 – Diagram showing Material embodied emissions (ktCO₂e) presented by material

Land

Land owned by Transport Scotland is estimated to remove and store around 9,500 tCO₂e per year, primarily through woodland sequestration. Other land uses, such as agricultural land, are likely to generate emissions. Estimates for land use impacts are currently high level, and further work is underway to improve understanding of this contribution.