Stockholm, a city which boasts its leading public transport system in Nordic countries, has a goal to be fossil free by 2025, said Lennart Hallgren, project manager in the Stockholm Public Transport.

"Our goal is to have a sustainable public transport system. We believe that getting more people into the public transportation will be environmentally friendly by itself," he said in a recent exclusive interview with Xinhua.

By the end of 2009, 130 biogas buses and 500 ethanol buses, the world's largest fleet of its kind, accounted for nearly 35 percent of all public buses in the capital of Sweden. The fleet will be further expanded by 700 new green buses.

The city is also testing on ethanol hybrid bus, which combines electricity and ethanol. Besides, all the rail traffic runs on renewable electric power from wind and hydroelectric power.

"The politicians decided to do it because there had been problems with air pollution and fossil fuel dependency. We want to reduce greenhouse gas emissions from the local transport system and get fossil fuel independent," Hallgren said.

Thanks to the green buses, public transport consumption of diesel has decreased by at least 12 million liters a year and emissions of fossil carbon dioxide have decreased by 27,000 tons a year.

"The first ethanol bus began service in 1989. So we have long experience with ethanol bus. It is bigger in volume, half produced from pulp and wheat locally and half imported from Brazil, which is produced from sugar cane," he said.

Today, a total of 500 buses, or about 25 percent of the total bus fleet, are running on the streets of Stockholm with ethanol, and almost the same infrastructure can be used to fill the tank.

"We started biogas bus in 2003 by signing a contract with the Stockholm Water Company, a sewage water treatment plant, responsible for serving Stockholm with clean water to drink and wash," Hallgren said.

"In the process of treating waste water, they have been producing raw gas for a long time. We signed a 20-year contract at pilot phase. We had a lot of problems such as filter and distribution at the beginning, but now the buses' biogas is guaranteed," he said, adding that the city will have 160 biogas buses by 2011.

Currently, Stockholm has three bus depots connecting with the sewage water treatment plants and the number will double in 2016, according to Hallgren.

Though biofuels are a bit costly, 8 percent more expensive than fossil fuel on average, it will be cheaper in the long run as the demand increases, he said.

Hallgren has also been in charge of the Baltic Biogas Project, which is a European Union project that involves 12 countries.

The project aims to spread information, share knowledge about biogas, and find new ways to produce and distribute biogas in the Baltic and other regions.