Gardner, Geoff and Francis Kuhn. (1992). Appropriate Mass Transit in Developing Cities (页面存档备份,存于互联网档案馆). Paper presented at the 6th World Conference on Transport Research, Lyon, June, 1992. p. 7. Retrieved March 11, 2010 from UK Department for International Development's Transport-Links Website.
Gardner, Geoff and Francis Kuhn. (1992). Appropriate Mass Transit in Developing Cities (页面存档备份,存于互联网档案馆). Paper presented at the 6th World Conference on Transport Research, Lyon, June, 1992. p. 7. Retrieved March 11, 2010 from UK Department for International Development's Transport-Links Website.