Restricting the volume of high-emitting vehicles roaming city streets carries many benefits, from clearing the air to quieting the urban din and beyond. Recognition of this simple fact has led to the proliferation of clean air zones, designated regions within a city where vehicles must meet strict pollution standards or pay a fee to operate within it. At last count, over 300 such areas had been established across Europe. In London, which boasts the largest ultra-low emissions zone in the world, a study has found a secondary benefit: Kids started walking and biking to school more.

In 2018 — the year before London’s rule took effect in the center of the city, and five years before the zone encompassed its entirety — researchers at the University of Cambridge and Queen Mary University saw in the impending policy an opportunity to conduct a natural experiment. They recruited children aged 6 to 9 and their families in central London and in Luton, a small city to the north, for a multi-year study to investigate how the program might affect a child’s health. Though research focused on understanding how lightening a city’s pollution load shaped the way young lungs develop, participants completed questionnaires alongside their annual health assessments. The responses allowed researchers to glean insights into their subjects’ activity levels, mental health, and other ancillary outcomes.

In the first of many papers expected from the study, the researchers found that, a year after the ultra-low emissions zone took effect, 2 out of every 5 London students in the study had switched from “passive” to “active” ways of getting to school. So instead of being chauffeured to school by their parents, the students started walking, biking, scootering, or taking public transit. On the other hand, in Luton, which acted as a control group, 1 in 5 made the same switch to modes that got them up and active, but an equal proportion switched to passive travel. But in London’s ultra-low emissions zone, shifting to driving was rare.

The implications of getting kids active, even if it’s just for their pre-class commute, are intuitive but important.

“Walking and biking and scootering to school is better for the child, better for the family, and better for the environment,” said Alison Macpherson, an epidemiologist at York University in Toronto who researches ways to protect and promote the health and safety of children. (She was not involved in the London study.)

“It’s a great way for children to start their day,” she said. “You can imagine just being thrown in a car and thrown out of a car is not the most calming way.” Walking or biking to school, on the other hand, can be calming and conducive to concentration, Macpherson said, potentially even improving academic performance. But perhaps most importantly, at a time when an epidemic of childhood obesity is on the rise worldwide, walking or wheeling to and from school can get kids more active.

“Physical activity in general is vital for preventing obesity,” said Christina Xiao, an epidemiologist affiliated with Cambridge University and lead author of the paper. “There’s strong evidence that shows that it prevents weight gain, and also has benefits in terms of children’s physical development and mental health as well.”

What exact health outcomes manifest among the cubs involved in the study will be a subject of forthcoming studies. One will attempt to tease apart what prompted parents to stop driving their kids to school. Xiao’s results demonstrate that the change took place, exploring why was beyond the scope of her study. So, whether the parents stopped driving because the daily fee of $16.50 (12.50 British pounds) made it cost prohibitive or because, with fewer cars on the roadways, parents felt safer letting their kids make the stroll to campus (or some combination of the two) remains to be seen.

Despite the benefits that stem from emissions-control zones like this, the legal environment in the United States has erected immense obstacles to replicating something like London’s ultra-low emissions zone. The closest anyone’s come was a voluntary and short-lived zero emissions delivery zone pilot in Santa Monica, California. And then there was New York City’s ill-fated congestion pricing zone, which Governor Kathy Hochul axed before it had a chance to woo the opposition.

While the legislative gordian knot tied by federal laws that preempt cities from establishing low emissions zones waits to be unwound, cities across the country can improve the infrastructure that enables people to embrace walking, biking, or busing, said David Reichmuth, a senior engineer with the Union of Concerned Scientists’ clean transportation program.

“We are on the way in making this switch from gasoline and diesel to electric vehicles, which is great,” Reichmuth said. “But really to meet our climate goals, we also just need to reduce the amount of driving. And these things that encourage or enable the ability for people to use active transportation are super important.”

While developing pedestrian-friendly infrastructure and building out protected bike lanes can encourage a shift in how people travel, Xiao found as she assembled a review of research investigating how to promote shifts to healthier transit, people preferred the stick to the carrot. In other words, discouraging car travel was often more effective than just building infrastructure conducive to active travel.

But whether it takes carrots or sticks to drive the shift, Xiao’s work adds yet more evidence to the argument that what is best for the health of the children benefits the health of communities and that of the planet as well. And, in the minds of those doing similar work, it underscores the urgency of getting fewer cars and more feet on city streets.

“Active transportation is sustainable transportation,” Macpherson said, “and we have to not lose sight of all of the benefits that come with making the commute to school easier to do in an active and sustainable way.”