Tradable credit schemes to decarbonize commuting trips: Insights from a field trial in a university setting

Tradable Credit Schemes (TCS) have been proposed as a market-based instrument for reducing transport externalities while allowing policymakers to address distributional concerns through the initial allocation of credits. Yet their effectiveness depends on how individuals respond to budgets, prices, and trading opportunities in real-world settings. Evidence from field experiments remains scarce. This paper reports results from a multi-week randomized controlled field trial of a CO 2 -based TCS for commuting. We implemented the MobilityCoins system with more than 600 participants in a university setting. The intervention assigned individual mobility budgets and priced commuting trips according to their CO 2 emissions across multiple travel modes. Our findings show that a TCS can be implemented in a real commuting context and can generate behavioral, distributional, and acceptability benefits. Treated participants reported more changes in commuting behavior than the control group, and econometric estimates indicate emission reductions for specific subgroups. The distance-based allocation produced progressive financial outcomes. The system was also evaluated favorably by a majority of treated participants. At the same time, emission reductions are not uniform across the full sample, and we find no clear evidence that participants responded systematically to variation in MobilityCoins prices. This suggests that the effectiveness of TCS depends on incentive salience, user understanding, and sufficient reduction potential in the target population. Overall, the study provides field evidence that TCS can be a promising and distributionally flexible instrument for sustainable commuting, while identifying key design challenges for future implementations.