<p>The effectiveness of interventions that aim to change travel behaviour is usually measured by the sudden shift from pre- to post-intervention. However, this binary perspective overlooks the gradual evolution of an individual’s travel behaviour over time. Our study challenges this paradigm and suggests the behavioural stages approach as a more precise tool for evaluating the efficacy of ‘soft’ travel behaviour interventions—those designed to influence perceptions, attitudes, and social norms or induce travel behaviour change through changes in the choice architecture. Many individual soft interventions could lead people to progress from a low stage like “pre-contemplation” to a higher stage like “preparation”—without resulting in behavioural change. Therefore, a more nuanced outcome measure is needed to assess individual soft interventions. An agent-based modelling framework is applied in this study to demonstrate the utility of the behaviour stage approach compared to traditional outcome measures. The findings show that the behavioural stages approach can detect the effects of interventions that more conventional measures like modal shift, travel frequency, travel distance, and attitudinal changes cannot detect. Moreover, the approach outlines the proportion of individuals who have progressed through stages, remained in the same stage, and regressed through stages post-intervention. The behavioural stage approach is thus a valuable tool for assessing the impact of soft interventions, and policymakers and decision-makers could devote more attention to this approach when evaluating travel behaviour interventions.</p>