1. World Health Organization (WHO): Air quality deteriorating in many of the world?s cities (2014).
http://www.who.int/mediacentre/news/releases/2014/air-quality/en/
2. United Nations (UN): Doha amendment of the Kyoto protocol (2015).
http://unfccc.int/kyoto_protocol/items/2830.php
3. International Energy Agency (IEA): CO2 emissions from fuel combustion (2012).
http://www.iea.org/publications/freepublications/publication/co2emissionfromfuelcombustionhighlights.pdf
4. Tegner, G.: Comparison of costs between bus, PRT, LRT and metro/rail (2003).
http://www.jpods.com/JPods/004Studies/CostPerMileOperations_UWa.pdf
5. Community Research and Development Information Service (CORDIS): Final report summary - EBSF (European Bus System of the Future) (2014).
http://cordis.europa.eu/result/rcn/140495_en.html