Purpose: Using a young driver sample, this experimental study sought to identify which combinations of threat-appraisal (TA) and coping-appraisal (CA) messages derived from protection motivation theory (PMT) participants would judge as most effective for themselves, and for other drivers. Method: The criterion variable was reported intention to drive within a signed speed limit. All possible TA/CA combinations of 18 previously highly-rated anti-speeding messages were presented both simultaneously and sequentially. These represented PMT’s three TA components: severity, vulnerability, and rewards, and three CA components: self-efficacy, response efficacy, and response costs. Eighty-eight young drivers (34 males) each rated 54 messages for perceived effectiveness for self and other drivers. Results: Messages derived from the TA severity component were judged the most effective. Response cost messages were most effective for females. Reverse third-person effects were found for both females and males, which suggested that combining TA and CA components may increase the perceived relevance of anti-speeding messages for males. Discussion: The findings have potential value for creating effective roadside anti-speeding messages, meriting further investigation in field studies.