Investigating the impact of London’s Ultra Low Emission Zone (ULEZ) on children’s physical activity and weight


This project is evaluating the impact of the introduction of London’s new Ultra Low Emission Zone (ULEZ) on primary school childrens physical activity and health, and to investigate potential pathways of impact.

The ULEZ is predicted to deliver major improvements in London’s air quality, reducing nitrogen dioxide and particulate exposures in central London.

ULEZ boundary 2019-2021 Source; Transport for London


Obesity and physical inactivity in childhood are two of the 21st century’s most serious public health challenges. The World Health Organization recently reported a tenfold increase in childhood and adolescent obesity in four decades. Inactivity and obesity are both distributed unevenly across the socioeconomic spectrum, creating a powerful lever to widen further health inequalities in later life.

To date, studies to increase activity and prevent/reduce obesity have focused on parental support and education, changes to school’s curricula and micro-environment for physical activity and nutrition. Little work has addressed the potential impacts of system-wide changes to the physical environment, reflecting the challenges of altering the physical environment and those of robust evaluation of health impact. This study addresses an important research gap – the pressing need for robust studies testing the impact of environmental improvement on children’s activity and obesity.

Low Emission Zones

Low Emission Zones (LEZ) aim to improve urban air quality via restrictions on vehicle use, additionally reducing traffic congestion and improving city environments, with the potential to alter family behaviours, including increasing active travel (such as walking or cycling to school) and outdoor physical activity. Because poor air quality occurs more frequently in areas of socioeconomic deprivation, LEZs may also lead to reductions in health inequalities. However, there is little data on the health impacts of Low Emission Zones. In summary:

  • Childhood obesity and inactivity present a global health challenge.
  • Little evidence exists on the impact of system-wide changes to the environment on child health
  • NICE, the House of Lords, and the Royal College of Physicians call for methodologically robust (i.e. prospective, longitudinal, controlled) research testing the effects of such interventions.

Research Design

This study is an offshoot of a major NIHR funded study – CHILL (Children’s Health in London and Luton) – which aims to find out whether reducing air pollution from traffic is good for children’s health – particularly the growth of children’s lungs, and on respiratory symptoms (like wheezing, sneezing, and coughing).

This work will make use of the wealth of data created by the CHILL study – a four-year prospective parallel-controlled cohort study, comparing lung growth in 1,560 primary schoolchildren in inner London with 1,560 schoolchildren in Luton (an area with similar poor air quality but with no low emission zone).

We propose to take advantage of this funded ‘natural experiment’ study to examine additionally the impact of this major environmental intervention on child physical activity and obesity.

We plan to use accelerometers to objectively measure physical activity levels of all study children and GPS monitors to track location/travel routes of a subset of children. Additionally, height and weight will be measured by trained research assistants, and travel mode to school assessed. This represents a unique opportunity of delivering a highly cost-effective and robust, controlled longitudinal evaluation, as requested by the above authoritative bodies.

What we are testing

We will test the hypothesis that the introduction of the ULEZ – a major system-wide environmental and urban regenerative intervention – will lead to increased physical activity, reduced obesity and reduced health inequalities in London primary schoolchildren.

Partners and collaborators

Our collaboration brings together researchers from four CLAHRCs (North Thames, West London, South London and East of England), the Centre for Diet and Activity Research (CEDAR) at the MRC Epidemiology Unit at the University of Cambridge, the MRC Asthma UK Centre in Allergic Mechanisms of Asthma, the Asthma UK Centre in Applied Research, and the MRC PHE Centre for Environment and Health.