In the sprawling metropolis of São Paulo, Brazil, home to 20 million people and a lackluster public transportation system, fighting through road traffic is a part of everyday life for commuters. With some 7 million vehicles already clogging city streets, and about a thousand more being added daily, it's not surprising that São Paulo offers a troubling example of how deadly car culture can be.

But while annual deaths from traffic accidents is quite high, it actually pales in comparison to another way cars are killing people -- from pollution.

According to a study commissioned by the Institute of Health and Sustainability, 4,655 people died as a result of air pollution in São Paulo in 2011. In that same time period, traffic fatalities accounted for 1,556 deaths. The study also points out that pollution contributed to over twice as many deaths that year than both Aids (874) and breast cancer (1,277) combined.

São Paulo air pollution particulates average 20 to 25 micrograms per cubic meter; over twice what is deemed safe by the World Health Organization.

Across the entire state of São Paulo, air pollution has been cited as responsible for the deaths of nearly 100,000 people from 2006 to 2011 from respiratory illness. As more cars are added to the road, and likewise more people move into the dense urban centers, that number is likely to rise -- both in Brazil, and throughout the world.