During the past few years, many people have come to realize that protecting the environment is not just something to think about, but something to act upon. Greenhouse gas (GHG) emissions contribute to global warming, and in the United States a large portion of GHG is released through transportation -- specifically, cars and trucks. The FTA released a great paper comparing the emissions from various forms of transportation and ways that transit agencies are working to increase the number of riders and reverse the effects of climate change.
http://www.fta.dot.gov/documents/PublicTransportationsRoleInRespondingToClimateChange.pdf
