We investigate the role of peer effects at the work place on the individual choice of transportation mode. We collect original data through an online survey on networks and sustainable behaviors among 334 individuals working in ten laboratories of the University of Grenoble Alps in February 2020. Using a linear-in-means model for binary outcomes and distinguishing endogenous and exogenous peer effects, correlated effects and network endogeneity, we find that peers have a significant and positive effect on individual active transportation mode’s choice. We show that in our setting, a simulated policy or intervention would be almost twice more effective in spreading active transportation mode through social spillover effects if it targets key players rather than random individuals.