In order to tackle this problem, cities are working together to make public transportation cleaner by adopting biogas and electric vehicles.

Sao Paulo City Hall has been investing in fuel alternatives since January 2009, when municipal buses started to operate with S-50 diesel. This type of fuel is more effective because it has low sulfur emission.

The city of Sao Paulo has a fleet of 15,000 buses that operate with S-50 diesel, polluting less than the S-500, the average type of diesel. There are 1,200 buses that operate with B-20 fuel, a mixture made of 20% biodiesel and S-50. Vehicles using B-20 reduce 22% of their emission of polluting materials, 13% of CO2 and 10% of hydrocarbon.

By the end of this year, 5% of the Traffic Engineering Company's (CET) car fleet will be electric. The company is responsible for traffic supervision and the idea is to have transit agents working with green cars, reducing the emission of greenhouse gases in the city.

The bus fleet is also being replaced by vehicles with more effective technology, capable of reducing the level of gas emissions. Around 60% of the 15,000 existing buses are new.

The city of Curitiba, in the South of Brazil, has also a public transportation fleet operating exclusively with biogas, the B-100, a 100% clean gas. The project started in 2009 with only six buses. In April, the fleet was increased to 24 vehicles and will be 140 by the end of 2012.

The citizens of Curitiba had an important role in proposing this public transportation system and the results are extremely positive. Compared to other buses, the ones operating with B100 pollute 50% less. With a continuous fleet renewal and the usage of biogas, Curitiba will reduce an average of 161 tons per month.