With the growing need to limit car dependence, public transportation appears as a key means of ensuring the transition to greener cities. However, access inequalities in undergrounds, tramways and buses are still considerable and intra-urban accessibility for all is still far from being achieved. Not only the usually labelled “people with reduced mobility (PRM)” but everyone could endure some types of barriers in their daily transit routes. The extent and severity of the resulting disparities are still seldom studied, accessibility being generally considered as the same for everyone. Conversely, this paper adopts a people-centered perspective to analyze and model constraints faced by selected vulnerable users in their use of public transport. We used mixed-methods, combining different survey and modelling techniques to enrich the usual accessibility approaches. The study is grounded in two cities—Brussels and Strasbourg —, enabling the development of adaptive metrics in various geographical environments. It focuses mainly on the impact of physical disability, visual impairment, old age and poverty on transit users’ behaviors. This approach leads to identifying failures and disincentives of each transport system. We conclude by discussing dissemination to transport operators and future research prospects.