1. Gulf Oil Company, Los Angeles, California, unpublished data.
2. Public Transportation Division, City of Tucson, Arizona,Monthly Transit Progress Report, January, 1976 to June 1976 and unpublished data.
3. R. J. Wallin and P. H. Wright, ?Factors Which Influence Modal Choice,?Traffic Quarterly, January 1974, pp. 271?289.
4. John T. Wenders, ?Two Forces Frustrate Transportation Change,?Arizona Review, June/July, 1974, p. 4.