<p>The rapid growth of e-commerce and urbanization intensity causes last-mile delivery challenges, including congestion, high emissions, and inefficiencies. Crowdshipping—leveraging public transport commuters to deliver parcels—emerges as a promising solution that aligns with urban sustainability goals. This study investigates the behavioral drivers of crowdshipping participation among train commuters in Australia using a mixed-methods approach grounded in the theory of planned behavior. A quantitative survey of 368 respondents is analyzed through binary logistic regression, revealing that factors such as environmental concern, income reliability, and social influence strongly predict willingness to participate. These findings are further enriched with semi-structured interviews of 19 logistics and mobility experts from Europe, Australia, North and South America, and Southeast Asia, which support transferability of the core design levers. Overall, the results underscore that integrating crowdshipping into public transport networks requires a focus on sustainable benefits, fair and clear compensation structures, and very little disruption to daily commutes. The study offers actionable recommendations for policymakers, public transport operators, and logistics providers aiming to develop integrated urban logistics solutions that effectively reduce congestion and environmental impact.</p>