6Whitt, J. A., G.Yago. Corporate Strategies and the Decline of Transit in U.S. Cities[J].Urban Affairs Review. 1985, (1): 37-65.
7Lowr, Sam, A Brief Portrait of Multimodal Transportation Planning in Oregon and the Path to Achieving It, 1890-1974[R]. Portland: Oregon Transportation Research and Education Consortium(OTREC). 2010.
8Vuchic, V,R. Transportation for Livable Cities[M]. USA: Center for Urban Policy Research, 1999.
9Research and Znnovative Technology Administration, Bureau of Transportation Statistics.Public Road Length, Miles by Functional System: 2005[EB/OL],http://www.bts.gov/publications state_transportation_statistics/state_transportation_statistics2006/html/table_0101. html.
10United States Department of Transportation. Bureau of Transportation Statistics[R]. American Travel Survey data, 1997.