1. CIA (2010). World factbook 2010. Central Intelligence Agency, Washington DC. ht tps://www.cia.gov/library/publications/the-world-factbook/index.html (accessed April 15, 2011).
2. IRF (2004, 2009, 2010). World road statistics. International Road Federation, Geneva and Washington DC.
3. Pears, A. (2005). Sustainability and roads: capturing the ESD opportunity. Urban Policy and Research, 23:2, 235-245.
4. Adams, W.M. (2006). The future of sustainability: re-thinking environment and development in the twenty-first century. Report of the IUCN renowned thinkers meeting, 29-31 January 2006. The World Conservation Union (IUCN), Gland, Switzerland.
5. Marsden, G., Kimble, M., Nellthrop, J., & Kelly, C. (2010). Sustainability assessment: the definition deficit .International Journal of Sustainable Transportation, 4:189-211.