As a child, Rebecca Unverzagt was always driven to school. Once she and her husband settled in London and became parents, their first instinct was that the family would now need a car. But after trying a car-less existence for a while, they realized they didn’t need it, and that it would be more trouble than it was worth.
Things became slightly trickier with their second child, because his nursery school was a 25-minute away from their home. Though she had previously been afraid to cycle in London, she picked up cycling as “my efficiency solution”: she could strap her son into his seat on her bike, transport him to nursery, leave her bike at an Underground station, and get to work. Now 12 and 8, her kids both walk 15 minutes to get to school, mostly on quiet streets.
Unverzagt is like many London parents who have to factor in expense, convenience, time, and safety into their decisions about how to transport their kids to and from school.
One policy that has affected this balance of factors for many Londoners is the ULEZ. ULEZ is a slightly awkward acronym for a congestion-pricing policy that London residents now know well: the Ultra Low Emission Zone, enacted in April 2019. Under the ULEZ, drivers of the most polluting vehicles (a minority of vehicles overall) are charged to drive within the zone.
The central London ULEZ was followed by two subsequent expansions of the ULEZ area, to now cover all of London. The ULEZ has exemptions for the cars of people with disabilities, licensed taxis, and community minibuses, among others.
Cars, which tend to be owned by wealthier residents of London, are the main contributor to air pollution in London. Half a million Londoners have asthma. Across the country, as many as 43,000 people are dying each year due to air pollution. Across the world, 8 million people die prematurely from air pollution each year.
In London, the ULEZ has featured prominently in politicized culture wars of recent years. In the 2024 London mayoral election, some of the angriest and most common criticisms of sitting mayor Sadiq Khan were complaints about the ULEZ—even though more Londoners supported expanding the ULEZ to all of London, compared to those opposed. Khan won re-election by a large margin.
According to the agency Transport for London, the ULEZ has helped to reduce roadside nitrogen dioxide concentrations by 53% in central London. A new study explores another benefit: changes to how children get to school.
A team of researchers from across the UK, and beyond, surveyed primary-school children inside and outside of Central London, before and after the introduction of the central London ULEZ in April 2019. Overall, they asked nearly 2,000 children how they had gotten to school that day, both at the 2018/2019 baseline and in 2019/2020. The follow-up occurred one year after the baseline, so that the results wouldn’t be clouded by seasonal variations in transport patterns, and to allow enough time for any changes in travel habits following the ULEZ.
The researchers compared Central London with Luton, a town near London with more limited public transport options than the capital. They chose Luton as the control group because it was similar to central London in terms of social and demographic traits and air quality. They felt it was also far enough away from the ULEZ zone that the policy change would not affect transport behavior in Luton (which did not have any similar policy planned).
54.1% of the respondents in London, and 89.7% in Luton, lived in a household with a car during the follow-up period. The researchers adjusted for aspects like car ownership and distance to school to strengthen the validity of the comparison.
The new paper, published in the International Journal of Behavioral Nutrition and Physical Activity, shows striking results. Compared to the baseline, 42% of the central London children switched from car-riding to active transport (walking, cycling, scootering, and/or using public transport). This was more than double the percentage of Luton children (20%) who made similar changes.
It’s unsurprising that clean air zones lead to less car use. Here, “it was surprising that it was mainly children living further away”, about half a mile or more, who made the change, says Christina Xiao, a researcher at the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge. Xiao, a lead author of the paper, points out that children living fairly close to school may have already been more likely to do the trip outside of a car. And for those traveling a bit further, “It could have been that [the ULEZ] was the additional impetus to encourage them to shift.”
The team is preparing a separate study on the reasons for shifts in travel modes, such as whether adults largely drove kids less for financial reasons or because it had become more safe and pleasant to walk, cycle, or scooter. It may be that fewer kids were driven simply because they were a year older, and were considered independent enough to get to school alone. This may partly account for why, even in Luton, one-fifth of the children studied switched from car-based to active transport during the study period.
Not all of the changes were in this direction. 5% of the central London children actually moved from active to passive transport. In Luton, 21% of the children transitioned to passive transport, so that essentially there was no change in rates of active transport.
Yet the overall change in London shows just one of the multiple benefits of the ULEZ. “Not only is it impacting transportation behaviour, but it’s really been having a demonstrable impact on our children,” Xiao says. However, while the study tracks changes following the implementation of the ULEZ, she acknowledges that transport behavior during this period could also have been influenced by other changes, for instance to roadworks, public transport, and other infrastructure.
School trips are important for several reasons. “School trips make up about one quarter of all peak morning hours,” Xiao says. “This can have a significant impact in terms of congestion, air quality, number of vehicles on the road.” This is an example of how reducing unnecessary driving can also lead to a better experience for drivers overall, since they have less traffic congestion to contend with.
A different study of London children on their way to and from primary school found that those travelling by car breathed in more air pollution than those who walked on back streets (though less than those walking on main roads). The same study found that parents’ biggest concern when it came to school travel mode was convenience, with health and environmental effects relatively unimportant. But learning about air pollution can change minds and behaviors, of both children and parents.
“Motorized transport negatively impacts children’s health in a variety of ways,” Xiao comments. An important one is physical activity. “Not only is physical activity important for healthy growth and physical well-being among children, it also plays a vital role in preventing obesity…In addition, air pollution and emissions from vehicles also are major threats to health and climate, and as air pollution’s effects have a stronger impact in children because they’re undergoing a period of lung development, it also contributes to childhood asthma.” Then there are the injuries and deaths resulting from road traffic.
Xiao concludes, “The ULEZ is one effective policy measure among many other complementary measures, including providing more accessible public transport and safer walking and cycling infrastructure.”
One of those complementary measures has been similarly politicized in the UK: low-traffic neighborhoods (LTNs), which place barriers to cars on certain small residential streets. During the Covid-19 pandemic, parts of London created school streets and LTNs that restricted driving and encouraged active mobility, as well as expanded cycle infrastructure. A study that the UK’s previous Conservative government commissioned of LTNs found that LTNs installed since the pandemic had substantially more supporters than opponents, and encouraged walking and cycling. Contrary to a common fear, they did not displace traffic to surrounding streets. Notably, more than half of people surveyed didn’t even know they lived in an LTN, attesting to how normalized these can become even after an initial outcry from a minority.
Unverzagt is part of Save Our Safer Streets, a campaign group that has been fighting for two years to retain the LTNs in the Bethnal Green neighborhood of East London. (The ULEZ expanded to this area in 2021.) Despite the pedestrianization of these spaces being supported by a majority of local residents, the council has decided to reverse it. The campaigners have brought the case before a judicial review, which will finally be heard in court in November.
The campaigning has come at some personal costs. Unverzagt has experienced threats on social media, some mentioning her children, for which she has had to get the police involved.
This is a microcosm of the political battles that continue to be waged over clean-air policies. From Cambridge, UK to New York City, cities have been considering similar policies to the ULEZ and LTNs, but also reconsidering them after public backlash where misinformation and emotions have run high. Xiao hopes that her latest study will help policymakers and publics make decisions backed by evidence.
Her other research suggests that combining “carrots” (such as bikeshare programs) with “sticks” (such as congestion pricing) may be more effective in stimulating active transport, compared to just either type of strategy alone. Unverzagt also feels that both types are needed. “People don’t like change,” she reflects. “So yes, you can make things attractive, and that is the preferred route, but sometimes you need to put something in and try it out.”
There are multiple reasons that Unverzagt appreciates streets with less traffic and airborne particles, in terms of her children getting to school. For children’s developing lungs, she points out, “The air pollution is a real problem. And because it’s invisible, it’s hard to keep front in mind.”
There’s another intangible benefit to her children being able to travel to school on their own. “It also matters to me because of independence,” Unverzagt muses. “If you sit in the back of a car and you’re just driven somewhere, it’s like someone putting you in a box and you magically appear somewhere else. They wouldn’t know how to get from A to B. So one way of becoming independent is navigating the space around you.”
