We propose and test several hypotheses derived from the expanded theory of normative social behavior (TNSB) that also includes collective norms (with descriptive and injunctive norms). Data come from a quasi-experiment intervention to promote safer driving among adolescents in Serbia. The intervention was administered among high school students, most of whom were on the verge of receiving their driver's licenses. Longitudinal data were collected from treatment and control schools at baseline (N = 1,449) and four months later at end line (N = 1,072). Descriptive norms at baseline predicted six-month changes in safer-driving intentions among women (β = .010 p < .05) but not among men. Main-effects of injunctive and collective norms were not significant. However, a significant interaction between descriptive norms and collective norms emerged among men (though not among women) and injunctive norms interacted with both collective norms and descriptive norms among women (but not among men). Initial evidence adds credence to the idea of enhancing the TNSB by adding both injunctive and collective (together with descriptive) norms as drivers of behaviors.