This study is a randomized controlled trial to investigate the effect of recurring reports on total external costs in the mobility context. The study included 777 participants from Switzerland who tracked their mobility using a GPS tracker app. Results show that the reports reduced the total of measured external costs (including health, congestion, and climate externalities) by 2.0%, though this reduction was not statistically significant. Climate related costs that include CO2 emission reduced by 5.7%. Reports with positive feedback led to reductions in external costs, while negative feedback had a "boomerang effect" with participants generating even higher external costs. The effects of the treatment diminished over time, resulting in no significant long-term effects. Finally, the average participant values the received feedback between 0.62 and 2.42 Swiss francs per report.