Thousands of children switched to walking or cycling to school following the introduction of controversial Ultra-Low Emission Zones in London, reveals new research.

Four in 10 youngsters in central London who previously went to school by car switched to more active modes of travel following the introduction of ULEZ, according to the findings.

In Luton, Bedfordshire, where there were no ULEZ, just two in 10 children made the switch during the same period.

London Mayor Sadiq Khan's flagship ULEZ programme, devised to reduce exhaust pollution, has been slammed by critics since its introduction in April 2019 for simply shifting traffic congestion elsewhere.

Several ULEZ cameras have been sabotaged by protestors.

But the new study, published in the International Journal of Behavioural Nutrition and Physical Activity, suggests that many more children in London are now making a more physically active journey to school.

A team led by researchers at the University of Cambridge and Queen Mary University of London analysed data from almost 2,000 children, aged six to nine, attending 84 primary schools in the capital and Luton. 

A total of 44 schools were located with catchment areas within or bordering London's ULEZ, and these were compared to a similar number in Luton and Dunstable. 

The inclusion of the comparison site enabled the researchers to draw more robust conclusions and increased confidence in attributing the observed changes to the introduction of ULEZ.

The team collected data from June 2018 to April 2019, prior to ULEZ implementation, and again from June 2019 to March 2020, the year after implementation of the ULEZ but prior to Covid-related school closures.

Among those children in London who travelled by car prior to the introduction of ULEZ, 42% switched to active modes, while five per cent switched from active to inactive modes.

In contrast, only 20% of children in Luton swapped from car travel to active modes, while a similar number (21%) switched from active to car travel. 

The researchers said that means that children in London within the ULEZ were 3.6 times as likely to shift from travelling by car to active travel modes compared to those children in Luton and far less likely (0.11 times) to switch to inactive modes.

The impact of ULEZ on switching to active travel modes was strongest for those children living more than half a mile from school.  

The researchers say that was probably because many children who live closer to school already walked or cycled there prior to ULEZ.

Study first author Dr Christina Xiao, of the Medical Research Council (MRC) Epidemiology Unit at Cambridge University, said: "The introduction of the ULEZ was associated with positive changes in how children travelled to school, with a much larger number of children moving from inactive to active modes of transport in London than in Luton.

"Given children's heightened vulnerability to air pollution and the critical role of physical activity for their health and development, financial disincentives for car use could encourage healthier travel habits among this young population, even if they do not necessarily target them."

Joint senior author Dr Jenna Panter, also of the MRC Epidemiology Unit, said: "The previous government was committed to increasing the share of children walking to school by 2025 and we hope the new government will follow suit. 

"Changing the way children travel to school can have significant effects on their levels of physical activity at the same time as bringing other co-benefits like improving congestion and air quality, as about a quarter of car trips during peak morning hours in London are made for school drop-offs."

Car travel contributes to air pollution which is a major cause of heart and lung diseases, including asthma.

It also limits children's opportunities for physical activity, hindering their development and mental health, and increasing their risk of obesity and chronic illnesses.

Despite UK guidelines recommending a daily average of 60 minutes of moderate-to-vigorous physical activity for school-aged children, less than half met these levels in 2021. 

In April 2019, ULEZ was introduced in London to try and to improve air quality by reducing the number of vehicles on the road that do not meet emissions standards. 

The central London ULEZ reduced harmful nitrogen oxides by 35% and particulate matter by 15% in central London within the first 10 months of its introduction, according to Transport for London (TfL).

After ULEZ was introduced in central London, the total number of vehicles on the roads fell by 9%, and by 34% for vehicles that failed to meet the required exhaust emission standards, with no clear evidence of traffic moving instead to nearby areas.

Study joint senior author Professor Chris Griffiths, of Queen Mary University of London, said: "Establishing healthy habits early is critical to healthy adulthood and the prevention of disabling long term illness, especially obesity and the crippling diseases associated with it. 

"The robust design of our study, with Luton as a comparator area, strongly suggests the ULEZ is driving this switch to active travel. 

"This is evidence that Clean Air Zone intervention programmes aimed at reducing air pollution have the potential to also improve overall public health by addressing key factors that contribute to illness."

The study was paused in 2020/2021, due to the introduction of Covid-19 restrictions in March 2020, and results are only reported for the first year of follow-up. 

But as both London and Luton were similarly affected, the researchers believe the disruption is unlikely to have affected the results.