(CNN) - Back to school season in the United States brings droves of big yellow school buses and crammed carpool lanes, but in other parts of the world, how children commute to class can vary widely.
In some remote fishing communities near Zamboanga City in the Philippines, schoolchildren row donated yellow school boats, provided through the Yellow Boat of Hope Foundation.
In Caracas, the capital of Venezuela, some children ride a gondola lift to school.
In the mountains of southwest China's Sichuan province, a steel ladder was constructed against a 800-meter bluff that children climbed to reach their boarding school in the isolated clifftop village of Atule'er.
Whether children hop on a school bus, row a boat or climb a cliff to get to school, how they commute can have major impacts on their health.
"Active commuting to school or work is a way of easily incorporating physical activity during the day," said Alejandra Jáuregui de la Mota, a researcher at the National Institute of Public Health in Mexico.
She defined active commuting as any transportation from one place to another that involves physical activity, such as walking, cycling, roller-skating or skateboarding.
"As a researcher, I am interested in understanding how people can engage in a healthy lifestyle," she said. "These habits are acquired during childhood."
Walking school buses and safe routes
Active commuting seems to be more of the past than the present, especially in the United States.
In 1969, 48% of children between 5 and 14 years old walked or bicycled to school, according to the National Center for Safe Routes to School. By 2009, that percentage had dropped to 13%. A report published by the US Centers for Disease Control and Prevention in 2016 found that in most schools, 10% or fewer students walked or biked in the morning on an average day.
Many parents report that their children do not walk to and from school due to distance or concerns about traffic, crime or weather, among other factors.
There have been recent efforts to ease parents' concerns and promote more active commuting.
In cities such as Chicago, groups have helped to establish safe routes for students to take to and from school. In others, such as in New Jersey, walking school buses involve children walking to and from school together, chaperoned by an adult.
About 25 million children in the US -- more than half of the nation's schoolchildren -- take school buses, according to the American School Bus Council. Some of these buses are even Wi-Fi-equipped.
Other students might commute to school by car or, in a big city, subway train. Now there are even the options of Uber, Lyft and other ridesharing services. (For most rideshare apps like Uber, the guidelines say you must be 18 to request a ride.)
Yet in other countries around the world, walking is the most common way children get to school.
Understanding 'the deep inequalities that persist'
As a child, "I would walk daily to get to school. When I was in preschool and throughout the first years of elementary school, my mom or dad would walk with me," Jáuregui de la Mota said.
"My house was not that far from school, but I remember saying 'hi,' talking or even playing with my friends who also walked to school," she said. "I can even remember the big old tree on the corner of my house or the sidewalk, which was not of concrete but ground."
In Mexico, one study analyzed data on 2,952 adolescents ages 10 to 14 and found that 68.8% walked to school and 2% rode bicycles. The study, published in the Journal of Physical Activity & Health in 2015, included data from the 2012 Mexican National Health and Nutrition Survey.
"Riding a bike with someone else -- their parent or relative -- was also a very common way to get to school," said Jáuregui de la Mota, who was first author of that study.
"Mexico is a very diverse country," she said. "Children may walk by themselves for hours to get to school, for example, more than three or four hours. They may get to school riding a horse or a donkey or even on a boat."
Similarly, in South Africa, 64.8% of students walk to school, while 9.5% travel by private car and 6.6% use a taxi, according to last year's General Household Survey conducted by the government's national statistical service Statistics South Africa.
The survey also showed that 11.1% use a vehicle hired by a group of parents, 3.6% use a bus, 2.8% use a bus provided by the school or government, 0.9% use a bicycle or motorcycle to get to school, and 0.5% use a train.
"There are still a number of primarily rural areas in South Africa where physical access to school remains extremely problematic, and children may be forced to use horse- or donkey-drawn carts, wade through rivers, cross dangerous roads or engage in other unsafe travel," said Julia de Kadt, a senior researcher at the Gauteng City Region Observatory in South Africa, who has studied trends in children's commutes.
"It's also critical to understand the deep inequalities that persist in South African schooling, which can be traced back to apartheid-era policy and practice," she said, adding that the inequalities have led to schools in historically white areas having certain resources that those in historically black areas lacked access to.
So children may travel far and wide to attend schools that provide a perceived higher quality of education due to those resources, but having the means to travel also varies, de Kadt said.
"The costs of children attending schools located far from home are extensive: long travel times, expensive travel arrangements, difficulty in fully engaging in extracurricular activities due to their commute, difficulty for parents in engaging directly with the school, attending a school that may be unwelcoming on the grounds of race group, culture or language and so on," de Kadt said.
"However, for many less-advantaged South African families who do not live close to high-quality public schooling options, this type of commute may well be their best option in ensuring social mobility for their children," she said.
"I attended primary school during the last years of apartheid," she added. "As a white child, I was privileged to attend an excellent public school less than a kilometer from home. Consequently, I usually took a quick and relatively safe unaccompanied walk to school."
Kids 'drop out of active travel' as they age
In Great Britain, about 46% of 5- to 10-year-olds and 38% of 11- to 16-year-olds walk to school, according to 2015 data from the Department for Transport.
However, 46% of those younger children but 23% of the older children go by car, and 35% of the older children but only 6% of the younger children take some other form of transportation, including the bus. The data showed that 2% of the younger children and 3% of the older children ride bikes to school.
Fewer older children might walk to school since many more primary schools might be located closer to home than secondary schools, said Ashley Cooper, a professor of physical activity and public health at the University of Bristol in England.
"Distances between home and secondary school are longer," said Cooper, who has conducted separate research on commutes to school.
"The longer distance means that kids drop out of active travel when they move to secondary school," he said.
Most children walk to school when the school is within 2 to 3 kilometers, or 1.2 to 1.9 miles, Cooper said. Any farther, most use a bus or car.
Cooper added that he remembers walking to primary school as a child, initially with his mother, and then cycling to secondary school.
"I mostly remember the bend outside the secondary school being treacherous when icy, with all the kids on foot lined up to watch the cyclists try not to fall off! But also, that I took off at lunchtime and after school with my friends on our bikes," he said.
"This fosters independence, which is important, and develops a habit for active travel," he said. "I still commute or do other journeys by bike some 40 years later."
Class is in session: What parents need to know
Researchers worry that a reduction in active commuting could contribute to the ongoing rise in childhood obesity, which the World Health Organization calls "one of the most serious public health challenges of the 21st century."
"There is a major problem of youth inactivity, leading to increased risk for obesity and chronic disease in adulthood," Cooper said. "The way that kids commute to school has a huge impact on their physical activity."
The CDC recommends that children and teens get at least an hour of physical activity each day.
An active commute to school could contribute to that daily exercise, and the American Academy of Pediatrics offers some tips on how to keep children safe as they walk or bike to school:
Children usually aren't ready to start walking to school without an adult until about fifth grade, or around age 10. Teach children about traffic signs, street signs and directions, and model correct behaviors when crossing streets. Consider starting a walking school bus by inviting families in your neighborhood to walk children together as a group. Adults may take turns walking the group. Make sure children stick to a safe route to school, one with well-trained adult crossing guards at every intersection. If walking without an adult, ideally children should walk with at least one other child in the neighborhood or older sibling. Make sure children know how to say "no" if a stranger offers a ride and know to yell and run for help if needed. Explain to children that it is not safe to use a cell phone or text while walking, because it makes them less aware of traffic and their surroundings. When cycling, make sure children know the rules of the road, wear a helmet and can check tire air pressure and brakes. Make sure the commute is during daylight.
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