This article describes intermediate stages in the development of TRAFFIC JAM, a computerized gaming simulation for children and adolescents. TRAFFIC JAMfocuses on the environmental and health impact of various means of transport, such as walking, biking, and going by bus or private car. It is being developed within the field of environmental psychology as a tool for promoting attitudes related to proenvironmental choice of transportation. So far, the program has been assessed in three empirical studies. In the first study, the background pictures were validated by means of semantic environmental description. Study 2 aimed to evaluate the hero figures in terms of Küller’s basic emotional process, and in Study 3, players’ emotional reactions to the first version of TRAFFIC JAMwere studied with both quantitative and qualitative methods. The important question of attitudinal change is not discussed in the article.