Abstract Commuting to work is often a highly habitual behavior that people perform automatically over a long period of time. Substituting an inactive with a more active commuting habit might thus support long‐term behavior change. This study investigated habit substitution processes in commuting behavior and related psychological determinants. We report primary analyses of an online planning intervention study conducted in Germany with a one‐arm pre‐post design over 14 weeks including multiple‐a‐day workday assessments across a baseline week followed by five post‐intervention measurement weeks. Forty‐two participants (60% female, M age = 32.3 years) reported daily automaticity, experienced reward and regret, and weekly plan enactment for new and old commuting behaviors. Multilevel models were fit. In this one‐arm study, automaticity of the old commuting behavior declined linearly, whereas the increase in automaticity of the new commuting behavior was more pronounced in earlier than later study weeks. Within‐person plan enactment and experienced reward were positively linked with automaticity of the new commuting behavior. Between‐person plan enactment was negatively linked with automaticity of the old commuting behavior. Weekly plan enactment and outcome experiences were associated with increases of new habits and decay of old habits in this study. Results warrant replication using an experimental design.