This paper addresses the two-way implication between punctuality level of public transport and commuter behavior. We consider a modal competition between public transport and an alternative mode. Commuters may choose different strategies to minimize their journey cost. In particular, when the bus becomes less punctual, more potential bus users arrive late at the bus stop. We show that punctuality increases with the alternative mode fare through a price effect. This specificity can be viewed as an extension of the Mohring effect. In the general case, the punctuality of a bus is lower at equilibrium than at optimum. According to the alternative mode operating cost, the bus attracts too many (small cost) or too few (large cost) customers.