1. P. Midgley, Urban Transport in Asia: An Operational Agenda, The World Bank, Washington, DC.
2. M. Walsh, Motor Vehicle Pollution Control in China: An Urban Challenge, Urban Transport Symposium, Beijing, China, World Bank and Asian Development Bank, Beijing, China.
3. World Bank Statistics.
4. United States Census Bureau.
5. C. Weaver, L.-M. Chan, Motorcycle Emission Standards and Emission Control Technology, The World Bank, Washington, DC, 1994, p. 3.