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2. Gilbert, Gorman and Dajani, Jarir S. 1975. “Measuring the performance of transit service”. Durham: N.C. Institute of Policy Sciences and Public Affairs, Duke University. Working Paper #475).
3. Schnell, J. B. “Performance measures of transit service: survey of operating costs and revenues of bus systems”. presented at the National Urban Mass Transportation Conference. December. University of Chicago.
4. International City Management Association (ICMA) and the Urban Institute. 1974. “Measuring the effectiveness of basic municipal services,”. Washington, D.C.: ICMA and The Urban Institute.