The Ultra-Low Emission Zone (ULEZ) - an overview

The expansion of the ULEZ will affect the way air quality impacts across London are assessed. Careful consideration will be required to establish appropriate input data and to interpret the results of air quality assessments. Some of the areas that will need to be considered include:

• Background Concentrations - Historically, background traffic-related pollutant concentrations in the UK have reduced over time, as cleaner vehicles become an increasing proportion of the fleet. The expanded ULEZ may lead to a step change in background concentrations. Using present-day measurements as an indication of the future baseline concentrations may be overly conservative. We'll be monitoring the results of annual air quality status reports produced by local authorities to determine how background concentrations change once the expanded ULEZ is implemented.
• Emissions – Defra’s Emissions Factor Toolkit provides forecasts. The current toolkit considers the ULEZ in central London, but doesn't include the impacts associated with the expansion in 2021 or the expansion in 2023. With the expected benefits of the expanded ULEZ, predictions using the current toolkit may be too high. A conservative approach may be useful for some projects, but if the future impacts are over-estimated it could mean that significant effects are incorrectly predicted, leading to the potential implementation of unnecessary mitigation. We'll use professional judgement to justify any divergence from the emissions factors drawn from the toolkit.
• Traffic - Traffic flows and fleet compositions extrapolated from pre-ULEZ expansion data may not be representative, either within or on the outside periphery of the expanded ULEZ. In some cases, it may be necessary to undertake sensitivity tests, where we'll work with transport consultants to build appropriate scenarios to model.
• Construction Dust - During the construction phase of a development, HGVs will be required to bring materials in and out of the construction site. The expansion of the ULEZ may influence the number of trips and the routes taken. This may affect the nature and scale of measures recommended to control and mitigate the risk of tracked out dust during construction works. Working with our clients, we'll determine the most likely routes that will be used by construction vehicles.