Integrating automated buses (ABs) into the public transport system may have potentials of providing more environment-friendly and cost-efficient mobility solutions by improving travel safety, reducing cost and decreasing congestion. However, the realization of the potentials depends not only on innovative technologies but also on users' acceptance of the ABs service. Whilst there has been a number of studies exploring the acceptance and adoption of ABs services, hardly any longitudinal studies have analyzed the long-term changes of individuals' behavior in adopting AB services. This paper aims to add knowledge on user acceptance of ABs in public transport based on empirical evidence in a real-life deployment context. Three waves of surveys that investigated users' travel attitudes and behaviors towards the automated bus were conducted at three different time points (six months, 11 months, and 14 months after the launch). The relationship between socio-demographic variables, travel experience variables, and attitude variables is modeled using structural equation modelling (SEM). Factors that influence experienced users to continue using the service were found to dynamically change over time. Initially, people were attracted to use the service if they perceived the information of the service to be sufficient, but they were demotivated to continue using the service if the comfort was worse, frequency was lower, or travel time was longer than expected. The results show that previous experience of adopting the ABs has impacts on different attitude variables. In order to promote individuals' continued use of ABs, the public transport authorities and operators should work closely to increase the frequency of the services. It is also necessary to enhance the comfort of the ABs.