The ability of a public transport system to provide regular services is the main attraction for the system users. Assessing the regularity of the provided services from the user's perspective is thus crucial for stakeholders in order to establish actions for maintaining or improving their system reliability level and therefore increasing the number of the public transport users. The purpose of this paper is to reveal the pertinence of the Gini Index based on the Lorenz curve as headway and travel time regularity indicator and to carry out a case study of the reliability of a bus operator of the city of New Delhi. We began by reconstituting the missed data in the provided automatic vehicle location data using an approximate approach and then, using correlation coefficients, we studied the linear relationships, before and after data reconstruction, between Gini Index and some of the most used regularity measures; headway regularity, headway adherence, standard deviation and travel time variability. Results show that headway adherence and standard deviation are the two indicators that have the higher correlations with the Gini index and that Gini index is less influenced by missing data and errors.