Pollution
One of the most harmful effects of traffic congestion is its impact on the environment. Despite the growing number of hybrid vehicles on the road, cars stopped in traffic still produce a large volume of harmful carbon emissions. Besides contributing to global warming, these emissions can cause more short-term and localized problems, such as smog and increased respiratory problems in a community due to poor air quality.
Read more : http://www.ehow.com/list_6308569_effects-traffic-congestion.html