YOKOHAMA--It’s common in Japan to see mothers transporting their young children on their bicycles, in child seats installed over the front and rear tires, and sometimes, strapped to them.

But a 16-month-old unhelmeted boy strapped to his mother’s chest died when their motorized bicycle fell on a rainy morning here, police sources said.

Experts and industry groups say the tragedy offers a warning for parents with small children.

The woman was also taking her 2-year-old son, who was sitting in the front child seat, to a day-care center.

She was wearing a raincoat and carrying an umbrella with its handle hooked to her left wrist, while pedaling the bicycle along a city road.

The bicycle tipped over with her younger son’s head hitting the ground and leading to his death around 8:25 a.m. on July 5. Her older son was safe, thanks to a bicycle helmet he was wearing, officials added.

Investigators ruled that the accident occurred because the umbrella got caught between the bike’s frame and fender beneath the handlebar.

The bike, which had two child seats installed above the front and rear tires, met safety standards. Some bags occupied the rear child seat at that time.

Police sent papers on Sept. 14 to prosecutors on the woman, who works as a caregiver at a day-care center.

On Oct. 12, however, the Yokohama District Public Prosecutors Office announced that it has decided not to indict her.

“I felt it was worry free to carry my child in front of me as I could see him,” an official quoted the woman as saying.

The Road Traffic Law prohibits two people riding a bike built for one rider, in principle.

However, the National Police Agency (NPA) set up a review committee for allowing a bike to carry two infants together in 2008 in response to parents’ complaints. They said that such a ban would make it impossible for them to pick up and drop off their children at a day-care center.

The committee compiled conditions in March 2009 to allow transporting two children at a time on a bike, such as that it be capable of carrying them safely.

The Kanagawa prefectural public safety commission set up detailed rules in July 2009 allowing cyclists to carry two children at a time by placing them in front and rear child bike seats.

The law allows them to carry a child strapped to their backs instead of using a child seat as long as a child is secured to the cyclist. But it does not allow or prohibit them from strapping a child to their chests.

The NPA said as for other prefectures, cyclists are allowed to carry a child on their backs but strapping a child around their chests is not mentioned.

Since the 2000s, front baby straps that free the parent’s hands have been popular. The reality is that a large number of parents who are rearing infants need to ride a bike while carrying their children strapped to the chests.

A 29-year-old woman, who resides in the city’s Naka Ward and is rearing a 2-year-old daughter, said, “It is difficult to carry my child on my back because she hates that and cries when I try to do so.”

A 34-year-old father, who lives in the city’s Hodogaya Ward and is raising a 3-year-old daughter and a baby girl who is not yet 1, said, “I have no choice but to ride a bike with my baby strapped to my chest to go shopping when I am busy.”

“If I carry my child on my back, his body touches the rear child seat,” another parent said.

Carrying a child on a parent’s back is not always safer than strapping an infant to the chest.

Safe Kids Japan, a nonprofit organization, jointly compared along with the Tokyo Institute of Technology the degrees of impact that a child suffers when a bike falls with the infant strapped to the parent’s back and to the chest.

The impact of a child strapped to a parent’s back exceeds that when they are carried on the parent’s chest by 20 percent.

The experiment also showed that in both back and chest carries, the force of the impact significantly exceeds the threshold where a 6-month-old baby can suffer a broken bone.

“If a cyclist straps an infant to the chest, it will be difficult to steer in various directions due to the existence of a child between the parent’s arms,” said Kazuo Yatagai, 67, curator at the Bicycling Popularization Association of Japan.

“A child is less secured to a parent in the case of the chest, compared with the back, making control of the bike less stable.

“It is also not safe to strap a child to the back because an infant can fuss and twist around. Using a baby buggy is the safest way to transport small children.”

The Bicycle Association (Japan) recommends that parents have their children wear helmets and strap them in with safety belts as a bike carrying three riders can easily become unbalanced. Furthermore, parents are advised not to transport infants who are younger than 1 on a bike because their necks are not strong enough to support wearing a helmet.