Understanding the route choice behaviour of public transport passengers is essential for explaining passenger preferences and predicting demand. A growing body of literature has focused on public transport systems without considering the relationship between choices in a new transport context and the inertia effect (the tendency to repeat familiar alternative routes). This is because significant changes in transport systems are infrequent and it is difficult to observe the same group of individuals before and after the change. This study aims to address these challenges by using revealed preferences collected through smart card data from the public transport system incorporating a new metro line in Santiago, Chile. An integrated discrete choice and latent class approach allowed the representation of the inertia effect. This helps us to understand its evolution over time and its effect on behaviour of passengers with different levels of adoption of the new metro line. The results show that variables such as the frequency of use of alternative routes, the last route chosen before the trip (stickiness variable) and changes in the transport context are crucial for the representation of the inertia effect. In particular, under stable transportation system conditions, the frequency of alternative choices is more relevant than the stickiness variable. However, under unstable conditions, such as when a new travel alternative is introduced, the stickiness parameter gains similar or even greater importance in explaining the inertia effect. On the other hand, the effect of a new transport context appears during the week of the introduction of the new metro line and the following week for both adopters and non-adopters. However, it persists in the following weeks only for adopters, suggesting that the impact of the context change is more significant for adopters, and in cases where they are observed to prefer their previous habitual options, this is mainly due to habitual tendencies or the inertia effect.