In 2015, Fort-de-France, the main city of Martinique, a small French West Indies island, made the ambitious decision to introduce a new mode of public transportation, a reserved public transport lane, or ‘RPTL’. Based on the Technology Acceptance Model, we conducted a survey to identify the determinants of intention to use the new mode of transport by current public transport users on the island. These determinants seem to vary depending on the frequency of use of the current transport system. Hence, when people already used public transport every day (high frequency), their intention to use the RPTL is solely predicted by the perceived usefulness of the RPTL. For those who use it less often (moderate frequency), only the norm―i.e., what others do―and age were predictors of intention to use the RPTL. Finally, for rare public transport users (low frequency), their intention is predicted by perceived usefulness and social norms. These results show that all users have different reasons for using this new mode of transport. Identifying these determinants could be useful to local politicians, enabling them to make efficient information and promotion campaigns for the RPTL, and especially designed for those potential users who are not familiar with public transport.