1. Inventory of U.S. Greenhouse Gas emissions and sinks: 1990-2012;U.S. Environmental Protection Agency,2014
2. Public transportation fact book;Neff,2013
3. The broader connection between public transportation, energy conservation and greenhouse gas reduction;Bailey,2008
4. EPA sets tier 3 motor vehicle emission and fuel standards;Environmental Protection Agency Office of Transportation and Air Quality,2014
5. Position paper: natural gas and C02 natural gas is a champion in road transport and also saving CO2 emissions;Gaudio,2009