Extensive national road safety campaigns are often supported by messages along roads/motorways or on matrix signs. The effect of these campaigns, and the specific contribution of roadside signs, is unknown. Research on this kind of public communication most often discusses whether the signs have a negative effect: distraction from the traffic task. Information on the distracting effect of roadside signs can be found in SWOV fact sheet Distraction in traffic under the question How distracting is roadside advertising?
Nonetheless, specific feedback on the current driving speed can affect road user behaviour. For example, with feedback signs on urban roads that inform road users of their current speed. Unfortunately, this effect is often temporary. See also the question How effective are speed campaigns?
