Assessment of real-world vehicle emissions in Scotland in 2021: Emissions testing campaigns in Edinburgh and Glasgow
Transport Scotland commissioned Hager Environmental & Atmospheric Technologies (HEAT), the International Council on Clean Transportation (ICCT), and Element Energy to conduct a remote sensing study to assess real-world vehicle emissions in four main cities in Scotland. These cities—Aberdeen, Dundee, Edinburgh, and Glasgow—plan to begin enforcement of the proposed low emission zones in 2023 and 2024. This report examines the real-world tailpipe emissions of vehicles in Edinburgh and Glasgow to assess how policies, including low emission zones, can improve urban air quality. Particular attention is given to the environmental performance of passenger cars, including taxis and private hire vehicles, that constitute the largest portion of vehicle activity in these cities.
Key findings from the study include:
- Passenger cars were the most predominant vehicle type and Euro 6 vehicles accounted for over 30% of all measurements.
- NOx emissions of diesel vehicles significantly improved after the introduction of the Real Driving Emission (RDE) Euro 6d-TEMP standard, showing an average 60% reduction from the preceding Euro 6 standards.
- Despite those improvements, post-RDE Euro 6 cars showed variable NOx emissions performance across vehicle families, as only a minority had mean real-world emissions below the RDE type-approval limit.
- The data provided further evidence of increased NOX and CO emissions from petrol vehicles with higher age and mileage. The results additionally showed that there may be a positive correlation between the ages and NOx emission performance of diesel vehicles, especially for those certified to below Euro 6.
The report provides evidence-based recommendations for further action beyond the policies already in place. These include expanding vehicle restrictions within the LEZs, implementing an age limit on taxis and private hire vehicles, and mandating garage inspections for certain classes of high-emitting vehicles.