The main purpose of this paper is to assess and gain a deeper understanding of the role of service quality in sustainable mobility. Specifically, the study aims to understand user perceptions related to service quality in urban public transport systems and to investigate whether they induce the adoption of adopt more sustainable behaviours for mobility purposes by opting for alternative means of transportation such as car-sharing, bike-sharing, and car-pooling instead of using one's own private car. Indeed, it is becoming vital for cities to investigate the norm of owning a car as a solution and to break this norm to allow citizens to stop using their car as an environmentally friendly solution. On the basis of the above theoretical assumptions, we develop a theoretical framework that aims to fill the literature gaps and is therefore oriented towards understand the linkage among the service quality of the urban public transportation system, service loyalty to urban public transport, the intention to use one's own private car less, and the intention to use sustainable means of transportation, mainly car sharing. An empirical investigation involving the city of Rome, Italy, is performed. The study proposes a territorial analysis and a qualitative and quantitative survey. The aim of this empirical study is two-fold: i) to learn the state of the art of the urban public transport system of the city under investigation and ii) to explore citizens' perceptions of the service quality of public transport and to understand their intentions to use public transport more, to use their own cars less and to adopt sustainable means of transportation such as car-sharing. PLS-PM statistical tools are used for data analysis. Our findings confirm that service quality has a direct effect on the intention to use public transport more and that this effect affects both the intention to use one's own car less and the intention to use sustainable means of transportation such as car-sharing more.