This article, the third in a series of four, deals with the processing and use of survey data to revise existing bus operations. The authors give details of the design processes at individual study level, and indicate the requirements for certain central studies of costs, patronage and revenues. Considerations associated with the selection of new services are outlined together with the implementation of results. The effects on the analysis of bus system parameters, externalities and patronage are described. Examples are given of bus running time problems, and the distribution of passenger journeys related to car ownership, sex, time of day and purpose. Costs are analysed to suggest relationships that could be used to determine the effect of changes in route, service levels and fares. Part 1 was published in Traffc Eng Control, October 1979, 20 (10), 471-4, Part 2 in Traffic Eng Control, November 1979, 20 (11), 541-5, Part 4 in Traffic Eng Control, January 1980, 21 (1), 14-20.