Clean Air Zones

Clean air is essential for life, health, the environment and the economy. In the UK, air pollution is the top environmental risk to human health. By improving air quality, we can reduce people’s exposure to pollutants such as nitrogen dioxide. Road transport is the largest source of such pollutants in urban areas.

A Clean Air Zone (CAZ) is an area in which a local authority has brought measures into place to improve the air quality. The creation of Clean Air Zones in urban areas is part of the government’s broader Air Quality Plan, which aims to improve air quality and address sources of pollution. There are two types of Clean Air Zones: non-charging and charging. In a non-charging Clean Air Zone, the focus is on improving air quality, without charging money for vehicles entering the zone. Measures can include retrofitting certain vehicles, traffic flow management, travel behaviour change and active travel improvements. In a charging zone, drivers will be charged a fee to enter the area if their vehicle fails to meet the required environmental standards.

Sweco has experience working with local authorities as well as with the Department for Environment, Food and Rural Affairs/Department for Transport’s Joint Air Quality Unit (JAQU) on both types of CAZ. We help to identify the best solution for a particular area in terms of the environment and economy, whilst achieving the requirements set by JAQU in the shortest possible time. We do this by drawing upon the expertise of our transport planning and environmental teams who gather data from multiple sources including Automatic Number Plate Recognition (ANPR) and through surveys and questionnaires to better understand how the creation of a Clean Air Zone could affect local businesses and the general public. This data is then used to update the transport and air quality models so as to forecast future traffic and air quality levels. The ANPR data also helps to identify the vehicle fleet mix in an urban area in order to determine which vehicles will be compliant and therefore not subject to a charge. The data collection and modelling work allows us to determine current and future air quality exceedances on the networks and produce the business case to fund these measures. Throughout the process, we engage with the various stakeholders to better understand the key issues and to refine the potential measures to address them.


• Air quality modelling
• Transport modelling
• Transport economics
• Transport appraisal
• Public transport
• Travel behaviour change
• Transport policy and strategy
• Stakeholder engagement
• Health impact assessments

For a European view of Sweco’s commitment to reduce air pollution, please read Sweco’s Urban Insight report Wholesome Air, Serene Cities - Reduced Noise and Air Pollution in Urban Areas here. The report was published in 2018 by our colleagues in Denmark.