As a rule, in order to achieve noticeable effects to the benefit of the environment, many persons have to change their behavior. To this end - besides the well-known classical control and command instruments and economic instruments - there are so-called intervention and diffusion instruments available. Intervention instruments work through a mechanism that changes psychological processes and aim to achieve behavior changes in the individual. Diffusion instruments, through their distribution mechanism, aim towards widespread penetration of the social system. The present paper reports on the conducting and evaluating of an environmental campaign that in a combined approach used intervention and diffusion instruments with the aim to induce behavior change in many people in a municipality. The object of the campaign was reduction of average driving speeds in a Swiss municipality. The campaign progressed through four phases: preparatory, diffusion, behavior change, and post phases.