Further explore the utility of protection motivation theory (PMT) in developing effective roadside anti-speeding messages.Via an electronic link, 81 participants holding a current Australian driver's license rated all possible pairs of 18 PMT-derived anti-speeding messages in terms of their perceived effectiveness in reducing speed for themselves, and for drivers in general.While some messages revealed third-person effects (perceived as being more relevant to drivers-in-general than to self-as-driver), others showed reverse third-person effects (perceived as being more relevant to self-as-driver than to drivers-in-general). Compared with messages based on coping appraisal components, those derived from threat appraisal PMT components (perceived severity, counter-rewards, vulnerability) were rated as being more effective, both for participants themselves as driver, and for drivers-in-general. Compared with females, males reported threat appraisal messages as being more effective for reducing speed in themselves (reverse third-person effect). Aggregate scores for the 18 messages derived from this ipsative methodology correlated modestly with those from a normative study using similarly-worded items.As jurisdictions globally recognize speeding as a major road safety issue, effective anti-speeding campaigns are essential. Findings added to current knowledge of PMT's efficacy as a basis for generating effective anti-speeding messages and indicated areas for future research and application.