This paper summarizes Mass Transit Systems (MTS) networks datasets, highlighting the lack of contribution on promoting access to opportunities and city-assets for the most vulnerable segments of the population. As case study São Luís, the city-capital of Maranhão holding the lowest average income in Brazil. Although social inequity issues seem ubiquitous in numerous Brazilian cities, this study reveals evidence of complications on social and spatial segregation being supported by a not reliable MTS service. It also produces an expensive and inefficient system, opening room for informal transports. Lack of subsidies constrains the system to provide a limited service to ‘On-Peak’ hours destinations, rising time-dependent users, and inhibiting the right to the city. A framework developed on system’s behavior analyze both ‘On-Peak’/‘Off-Peak’ periods identified deficiencies hidden behind MTS network’s capillarity, resulting in evidence of social exclusion and spatial injustice promoted by long headways, which does not ease access equally the city.