In a large-scale natural experiment with over 14,000 individuals, we investigate whether public transport usage can be influenced by social norms and by economic incentives. Despite their effectiveness in other domains, we find a tightly estimated zero for descriptive social norms on ridership. Increasing the economic incentive, by doubling the trial period, significantly increases uptake and long-term usage. This increase is sustained for months after removing the incentive. The effect is mainly driven by initial low users, which is evidence for habit formation and highlights the heterogeneous effects of the policy. While there is scope for long-term behavior change, norm nudges might not be the most promising approach.