Road traffic is a major source of air pollution in London, posing serious health risks. One in 11 children in the city has asthma, a condition worsened by poor air quality. Car use also limits opportunities for active travel, such as walking and cycling, which help prevent obesity and chronic illness.

Introduced in 2019, the ULEZ charges high-polluting vehicles that enter all London boroughs. According to Transport for London (TfL), it has reduced levels of the pollutant nitrogen dioxide (NO?) by 53% in central London, 24% in inner London, and 21% in outer London, while also cutting traffic.

The research published today inBMJ Open -- led by scientists from the University of Cambridge and Queen Mary University of London -- examines the ULEZ's impact on school travel. This work is part of the Children's Health in London and Luton (CHILL) Study, which previously found that 42% of children who travelled by car switched to active travel modes after the ULEZ was introduced. Through in-depth interviews with 21 families from the CHILL study and seven teachers from CHILL schools, the researchers identified key drivers of change and ongoing challenges in adapting to the policy.

Families reported the rising costs of car travel and reduced convenience made active travel more appealing. Those who already walked or cycled discussed how improved air quality made the journey more enjoyable and healthier. With less traffic, some families took longer scenic routes home, which meant they spent more time together being active. Teachers observed fewer asthma related symptoms among students and noted that safer streets encouraged more outdoor play.

Despite its benefits, adapting to the ULEZ has been hard for many families outside central London. The scrappage scheme helped some families to upgrade their vehicles, but it was not enough to fully cover the cost of a new ULEZ compliant car. Public transport was often described as expensive or poorly connected in these areas. Some families parked outside the zone and walked, while others felt forced to continue driving as it remained the most affordable and convenient option. The study highlights inequalities in access to cleaner, greener travel, calling for faster investment in affordable, well-connected transport options across all boroughs.

Dr Olivia Alliott, lead author from the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, said: "Policies like the ULEZ play a crucial role in promoting a healthier school journey for many families. However, a fundamental part of their success is making sure that everyone experiences these benefits by ensuring such policies are implemented alongside accessible and affordable alternatives to driving.

"Our previous work found that the ULEZ has encouraged children to take up walking and cycling to school. This work identifies some of the possible reasons for that, and highlights both the positive and negative experiences of the ULEZ which are reflected in an individual's ability to pay the charge and the alternative travel modes available"

The study reinforces the importance of policies like the ULEZ in shaping healthier, sustainable cities while also ensuring that solutions are inclusive and equitable. It offers valuable insights for policymakers worldwide considering similar initiatives to improve air quality and public health.

Joint senior author Professor Chris Griffiths from the Wolfson Institute of Population Health, Queen Mary University of London, said: "This important study brings yet another perspective telling us how the ULEZ can affect the way families can live, travel and experience the environment. These systemic effects on society go beyond simply 'cleaning the city air'"

The interviews were conducted between November 2022 and March 2023, and the results do not include experiences of the ULEZ expansion in August 2023 to cover the majority of Greater London.

The study was funded by the National Institute for Health and Care Research (NIHR), NIHR Applied Research Collaboration North Thames and the Medical Research Council. The study was conducted in collaboration with Queen Mary University of London, Imperial College London, University of Bedfordshire, University of Exeter, University of Edinburgh, University of Oxford and University of Southern California.

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