"His voice and whistle were very loud and he could be heard even above horns of vehicles,"Tian recalls, adding that he also saw the policeman several times in rainy and snowy weather.

Out of curiosity, Tian, as a reporter then, interviewed Li and discovered the police officer's insights into traffic safety.

Inspired by Li, Tian founded a volunteer organization called Qingdao Voluntary Road Rescue Team in 2014, aiming to provide roadside services and assistance, as well as promoting positive driving habits in the city. Li soon joined the organization. He was seen many times helping drivers with broken-down vehicles and even the occasional car fire.

Road safety was always high on Li's working agenda.

It cost him more than 20,000 yuan ($3,134) out of his own pocket to learn 3D animation on the computer, which he applied to a multimedia course that sought to spread traffic safety knowledge through lifelike presentation.

The local police authority says Li gave over 400 lessons to more than 140,000 people, including his fellow officers, workers and schoolchildren.

In 2012, he had opened a personal account on the Chinese microblogging platform, Sina Weibo, publishing frequent posts regarding traffic conditions and regulations and answering questions from other users.

The account had more than 30,000 followers and some of his posts have been forwarded, commented upon and liked 149,000 times.

"The more people get to know the traffic laws and understand road safety, the easier it is for traffic police to do their job," Li once said.

Li participated in social charity initiatives regularly, donating money and giving blood. Sometimes he would escort injured people to hospital.

However, Li's kindhearted nature didn't mean he would be benevolent to traffic violations. Instead, he punished offenders without hesitation and in line with the law.

He administrated more than 50,000 traffic violation penalties, according to data from the local police authority.

At home, Li was a devoted husband and father, who enjoyed life and had childlike qualities, according to Li's wife, Chen Ying.

"At the top of a refrigerator there are two toy guns, which we would frequently play with for fun," says Chen, adding that her husband also liked playing hide-and-seek with her.

"We had planned to take a self-driving tour around the country after he retired in five years," Chen says.

"The day my father died was my birthday according to the Chinese lunar calendar," says Li Sheng, the couple's daughter, adding that he would always be in their heart.

His professional legacy lives on, too, through his colleagues around the country and on the roads of the city he proudly served, one helpful gesture at a time.

Hu Qing contributed to the story.