O objetivo principal da tese é buscar critérios que orientem e justifiquem a definição de estruturas tarifárias para o transporte público urbano, diferenciando valores relativos de tarifa segundo o tipo de uso do sistema de transporte e as características do usuário. Após uma análise dos objetivos do transporte público urbano, foram considerados relevantes os critérios de eficiência econômica e equidade para a elaboração e avaliação de estruturas tarifárias, por sua relação direta com o bem-estar social. Para satisfazer critérios de eficiência, os preços devem ser determinados segundo o custo social marginal de curto prazo, considerando, porém, falhas do mercado de transporte público que levam a preços ótimos que desviam de forma sistemática dos custos marginais. Os critérios de equidade, por vezes restritos a consideração de aspectos de distribuição de renda, devem ser complementados pelo critério de necessidade de transporte, indicada pela categoria sócio-econômica do indivíduo e sua família. Um modelo conceitual para elaboração e avaliação de estruturas tarifárias é proposto, cujo objetivo é maximizar uma função de equidade, sujeito a restrições que contém informações sobre estruturas tarifárias que refletem critérios de eficiência ou outros que os condicionem.

The major objective of the thesis is the search for criteria for guiding and justifying the definition of public transport fare structures. The latter should be interpreted as the processo f differentiating relative prices according to the type of use one makes of the system and the characteristics of the user. An analysis of the objectives of urban public transport led to the choice of economic efficiency and equity as relevant criteria for the design and evaluation off are structures: this is based upon the fact that these criteria have direct impacto n social welfare. The adopted approach recognizes that public transport is a multiproduct economic activity offering several services - trips between many origins and destinations, at different times and on various types of days - with different costs. Users make different uses of the service, consuming distinct products. The demand for the many products offered by a transportation system oughr to face proces that satisfy the criteria for economic efficiency, if social welfare is to be maximized. On the other hand, one must acknowledge the existence of differences between the consumers of trnasportation services - income, auto availability, sex, age and family structure - which define their constribution capabilities and their transport needs. Equity criteria are required if one is to account for the differences in userscharacteristics. Efficiency criteria ask for short run marginal cost princing. However, there are some important failures in the public transport market: consequently, optimal prices should deviate systematically from marginal costs. The structure of marginal costs, concerning the many different products, and the nature of the optimal deviations provide important information for fare structure design. Equity criteria are sometime interpreted as concerning income distribution issues alone. A wider view of the equity concept indicates that, for the purpose off are design and evaluation, transport needs related criteria, as reflected by the sócio-economic category of the individual and his family, should be considered in addition to income distributional aspects. A conceptual model for design and evaluation off are structures is proposed. The objective is to maximize an equity function, subject to constraints that convey information about efficient fare structures and other informal criteria. As an important feature, the model considers that the application of equity criteria to public transport fare structures requires that family characteristics be taken into account besides the individual.