1. Texas Commission on Environmental Quality (TCEQ). Agency Activities: Air Quality (FY2011-2012). 2013; http://www.tceq.texas.gov/publications/sfr/057_12/air. Accessed on 6 September 2013.
2. Texas Commission on Environmental Quality (TCEQ). Ozone: The Facts. 2013; http://www.tceq.state.tx.us/airquality/monops/ozonefacts.html. Accessed 6 September 2013.
3. U.S. Department of Transportation, Bureau of Transportation Statistics. Texas Transportation Profile. 2002; http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/state_transportation_statistics/texas/pdf/entire.pdf. Accessed on 17 April 2011.
4. City of Houston. Houston Facts and Figures. 2013; http://www.houstontx.gov/abouthouston/houstonfacgts.html. Accessed on 6 September 2013.
5. Greater Houston Partnership. Houston: Energy Powerhouse. 2013; http://www.houston.org/assets/pdf/opportunity/Energy-Data-Sheet.pdf. Accessed on 6 September 2013.