A new law has taken effect in Vietnam requiring all motorbike riders to wear helmets. Motorbikes are the most common form of transportation in Vietnam, but drivers long refused to wear helmets, leading to huge numbers of traffic fatalities. In Hanoi, Matt Steinglass has more.

The sound of a Vietnamese city is the sound of motorbikes. In Hanoi and Ho Chi Minh City, motorbikes account for more than 90 percent of all the vehicles on the road.

But for decades, most Vietnamese riders refused to wear helmets, which they derisively call "rice cookers". Traffic safety advocates wondered what it would to change people's behavior.

On Saturday, they got their answer.

Traffic police officer Nguyen Ngoc Hieu says according to Government Decree Number 32, from December 15, everyone riding a motorbike anywhere in Vietnam, including passengers and children, must wear a helmet. He says the government is doubling the traffic police force to more than 1,000 officers to enforce the new law.

Hieu spoke Friday at the entrance to Hanoi's Long Bien bridge, one of the busiest intersections in the city. It was the day before the new law took effect, but at most, only a quarter of the riders were wearing helmets.

Nguyen Van Hoa, a public security official at the People's Committee in the Hanoi neighborhood of Ba Dinh, says the helmet campaign is going slowly. Hoa says at one local primary school, many parents hadn't bought helmets for their children. He says this had made officials angry.

Meanwhile, the sidewalks of Hanoi are crowded with helmet vendors doing a brisk trade as people try to comply with the new law.

Longtime helmet shop owner Nguyen Nga Thao says her sales are up more than 10 times, to about 2,000 helmets a day.

Thao says helmets have become much more fashionable since September, when the new law was announced. The new ones are lighter, with designs such as hibiscus flowers and panda faces, for female riders who would not have bought a helmet before.

Nguyen Thi Bao owns Ba Café, a fashionable coffee shop. She says she just bought her first helmet, a green Piaggio model, to match her green Piaggio motorbike.

Bao says she would still prefer not to wear one. With such beautiful hair, she says, how can I wear a helmet when I go out at night?

Government Decree Number 32 took effect at six o'clock Saturday morning. By noon, it was clear that compliance rates were more than 99 percent. In one night, Hanoi's streets had become a sea of brightly decorated motorbike helmets.

Dang Van Binh, 52, has driven a "xe om", or motorbike taxi, for 13 years.

Binh says in the entire morning, he had seen only a few drivers without helmets. He says several were stopped by police and fined - 150,000 dong, or about $9, more than the price of a cheap helmet.

Le Huong, 25, was wearing a helmet for the first time.

Huong said she still thought helmets were ugly, and was only wearing them because of the law.

Then Huong's friend Hong, who was driving the motorbike, explained in English.

"The government, they approved for all the people to follow, and we are Vietnamese and we are the good ones, so we follow," said Hong. "We are Vietnamese, and we love our country. So we follow our government."