“Santiago de Chile is implementing a new urban transport system that may give important incentives for other world cities”. This World Bank citation refers to the sophisticated public urban transport system called Transantiago started in February 2007. It represents the answer of the national government on the eminent traffic problems in the metropolitan area of Gran Santiago which are ought to continuously growing motorization rates and vast spatial expansion. Specific emphasis by the public authorities is put on the social benefits expected from the new urban transport policy. Taking into account the high correlation of social inequalities and spatial segregation within the city, the accessibility for low income households should be improved and social exclusion should be combated. Within this context the integration of land use and transport policies plays an important role. But as there does not exist any explicit definition for the key term “social inclusion by accessibility improvements”, it is unclear how the actual planning output can be measured and the social gains of the Transantiago system be assessed. However, the experiences with the new system in the first months have been merely negative due to a set of technical, capacity, organizational and information-related problems. The paper consists in five basic parts. After a short insight into the topic, the theoretical framework is presented and the key issues are defined, in order to then present the methodological approach perceived as appropriate for evaluating the specific Santiago case. This approach is based on a set of quantitative and qualitative methods which will be implemented in frame of a PhD thesis related within the next years. The third part consists in the summary of the very first research results which already may give a hint on the explanatory variables for the role of a public urban transport system in the context of social inclusion. The results so far will are particularly related to the case before the Transantiago implementation. The final conclusion part offers some ideas which elements are to consider within a model that presumes to describe the role of public urban transport in frame of social inclusion.