1. Domencich, T., and Kraft, G. (1970). Free Transit. D.C. Heath & Company, Lexington, Massachusetts.
2. Kemp, M. A. (1973). ?Some Evidence of Transit Demand Elasticities,? Transportation 2: 25?52.
3. Wong, H.-K. (1971). ?Some Demand Models for the Taxicab System in the Washington, D.C. Area,? Urban Institute Working Paper 708-39, Washington, D.C.
4. Meyer, J. R., Kain, J. and Wohe, M. (1965). The Urban Transportation Problem. Harvard University Press.
5. Kirby, R. F., Bhatt, K., Kemp, M., McGillivray, R. and Wohl, M. (1974). Para-Transit: Neglected Options for Urban Mobility. The Urban Institute, Washington, D.C.