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China is historically known as the "Kingdom of Bicycles", yet following the country's opening up and the steady increase in the average salary, many people have swapped two wheels for four.

When bikes ruled the road in 1986, about 40 percent of cyclists had to travel more than 45 minutes to reach their destination, said professor Duan.

"The common accepted range for commuting by bicycle is only half an hour, though," he said, which explains why so many people quit riding as soon as they could afford a car.

Take the Volkswagen Santana, the best-selling car in China, with more than 3 million sold so far. When the model made its debut in 1983, urban per capita monthly disposable income in Beijing was 49 yuan, putting its 200,000-yuan price tag far out of reach of most people.

However, the city's urban per capita monthly disposable income now tops 2,228 yuan ($332), while to drive away in a brand new Santana costs just 100,000 yuan.

"The living standard has been improved and people have become lazy," said Jiang Shengqi, who manages a bicycle rental point outside one of the entrances to Lama Temple subway station in Beijing. "People are now more likely to buy electric bikes."

About 30 percent of all journeys made in 36 key cities in 2008 were made by bicycle, according to a study led by Wu Hongyang. To boost that figure, promotions have been launched across China to raise awareness of the positive impact cycling has on the environment and an individual's health.

Among the biggest initiatives is Car-free Day, which is organized by the Ministry of Housing and Urban-Rural Development. It will be observed for the third time with events in 112 Chinese cities on Sept 22.

In Beijing, less than 40 percent of all car journeys are less than 5 kilometers, according to Beijing Transportation Research Center.

Li Bingren, chief economist for the ministry, said the average cyclist can reach speeds of up to 14 km/h, making bicycles a far more efficient and "green" form of transport for short and medium distances.

As commuters spread further out into the suburbs and satellite towns, promoting bicycle use could be crucial to easing traffic congestion and reducing carbon emissions.

With this in mind, many cities have attempted to become more bicycle-friendly. However, early efforts to boost rental services hit problems when the expected boom in business failed to materialize, causing many firms to fold.

"The profit margins are too low to maintain a business," said Bai Xiuying, manager of Bei Ke Lan Tu, the first bicycle rental company in Beijing, opening in 2005. The company hit a peak during the Olympic Games in 2008, when it had 200 rental shops offering more than 8,000 bicycles. Today, only 12 shops remain.

Beijing transport officials have announced plans to actively promote rental services outside selected subway stations along Line 4 and Line 5. Rental points will be set up every 500 meters and, by 2012, it is hoped commuters and tourist will have access to 20,000 bicycles at 1,000 sites.

"We're confident about the future, and that's why we've made an additional investment of 10 million yuan (in the business)," added Bai.

Authorities in Hangzhou, a picturesque tourist destination in Zhejiang province, introduced rental stations in 2008. Anyone aged 16 to 70 has access to up to 50,000 bicycles parked at 2,000 stations across the city - and the ride is free if the bicycle is returned in an hour.

Rental points are found within every 300 meters in the downtown area and have proved so popular that the service attracts an average of 250,000 users a day.