London-wide ULEZ Six Month Report

There is a well-established and ever-growing body of scientific evidence linking exposure to air pollution and a number of adverse health effects across all stages of life, with these effects seen even in relatively low air pollution environments.

In 2021, the World Health Organization (WHO) updated its air quality guidelines, recommending more stringent guidelines to protect public health. The updated WHO air quality guidelines are more ambitious than the UK national legal limits and emphasise that no safe level of air pollution exists.

On the 29 August 2023, to help tackle air pollution in the capital, the Mayor of London expanded the Ultra Low Emission Zone (ULEZ) across all London boroughs.

The ULEZ boundary is now the same as the boundary for the Low Emission Zone (LEZ) for heavy vehicles. The London-wide zone measures 1,500 km² and covers nine million people, making it the largest zone of its kind in the world.

This report covers the first six months of the newly expanded scheme and provides preliminary analysis of air pollutant emissions and concentrations, building on the previously published London-wide ULEZ First Month Report.

The method used for analysing the preliminary impact on concentrations builds upon a previously peer-reviewed method. Fuller analysis of both emissions and concentrations will be reported in the One Year Report, which will be supported by an advisory group of external experts.

As well as preliminary analysis of pollutant emissions and concentrations, this report provides an update to the “compliance rate” of vehicles detected travelling in the zone that are subject to the ULEZ – that is cars, vans, minibuses, and motorcycles. The compliance rate is the share of vehicles detected in the zone that meet the ULEZ standards.

The findings indicate that the Mayor’s air quality policies, and in particular the ULEZ and LEZ schemes, are having an important impact on reducing the number of older, more polluting vehicles seen driving in London and on reducing the levels of harmful air pollution that Londoners are exposed to. In summary, the key findings are:

• Pollutant emissions across London in 2023 are dramatically lower than expected if we hadn't expanded the ULEZ London-wide.
  • Nitrogen oxides (NO_X) emissions from cars and vans in outer London are estimated to be 13 per cent and 7 per cent lower compared to a scenario without the ULEZ.
  • There has been a saving of 424 tonnes of NO_X in outer London.
  • PM_2.5 exhaust emissions from cars and vans in outer London are estimated to be 20 per cent lower than they would have been had we not expanded ULEZ to outer London.
• ​​​​These emissions reductions are improving air quality. In the first six months of operation, roadside nitrogen dioxide (NO₂) concentrations in outer London were up to 4.4 per cent lower than would have been expected without the London-wide ULEZ expansion.
• All ULEZ policies in total have had a dramatic impact on improving air quality across the capital. Harmful roadside NO₂ concentrations are estimated to be:
  • 21 per cent lower in outer London than they would have been without the ULEZ and its expansions.
  • 53 per cent lower in central London than they would have been without the ULEZ and its expansions.
  • 24 per cent lower in inner London than they would have been without the ULEZ and its expansions.
• Long term trends indicate that average concentrations in all London zones improved at a faster rate than the rest of England average over the same time period. This is particularly notable in outer London where concentrations have improved more rapidly over recent years and are now similar to the rest of England average, which has historically been lower.
• Areas outside London are also seeing the impacts of the ULEZ, with roadside NO₂ concentrations within 5 km of the Greater London boundary on average nine per cent lower in 2023 than an estimated “No ULEZ” scenario. As this is an average for the whole boundary zone, this means that some roads will be seeing even greater reductions.
• A larger proportion of vehicles recorded driving in London are cleaner. The London-wide compliance rate for vehicles subject to the ULEZ standards after the first six months was 96.2 per cent, up from 91.6 per cent in June 2023 and 39 per cent in February 2017, when changes associated with the ULEZ began.
• Compliance rates have increased for both cars and vans; 97.1 per cent of cars and 88.9 per cent of vans seen driving in the London-wide ULEZ met the standards after six months of operation, up from 93 and 80.2 per cent in June 2023 and 44 and 12 per cent in February 2017.
• There are fewer older, more polluting ULEZ vehicles seen driving in the zone. On an average day, there were 90,000 fewer non-compliant vehicles detected in the London-wide ULEZ in February 2024 compared to June 2023. This is a 53 per cent reduction in non-compliant vehicles between those dates.
• In the expanded outer London area, ULEZ vehicle compliance is now 96.2 per cent, up from 90.9 per cent in June 2023. This is nearly the same level of compliance as seen in inner and central London, with 96.5 per cent and 96.4 per cent, respectively.
• In outer London, over 97 per cent of cars now meet the ULEZ standards, up from 92.4 per cent in June 2023. Van compliance in outer London has increased by 9.5 percentage points, now 89 per cent, up from 79.5 per cent in June 2023.

Read the preliminary evaluation of the impacts of the London-wide ULEZ, six months following the ULEZ expansion to outer London.