This study has used SEM with latent variables to process UK NTS data in order to examine the time aspects of immobility by analysing the articulation between days when respondents do and do not make trips. SEM makes a substantial contribution to the work both in terms of data processing and of the resulting knowledge of inequalities in mobility. First the constitution of latent variables proved a good way to process trip characteristics. Trips are characterized by many observed variables, especially in a survey over several days in which the time aspect must also be considered. Lastly, the SEM proposed is distinctive in its capacity to take account of multiple relations, in particular in the context of Confirmatory Factor Analysis (CFA). We have thus been able to show that although immobility on a weekday can be partially offset by more trips on other weekdays for some reasons, no set-off is observed at weekends, whether respondents are in the working population or not.