Usually attempts to influence driving behaviour are based on negative consequences for unsafe or undesired behaviour, e.g. fines. In line with this general tendency to induce negative consequences are means like speed ramps in speed-30-areas which force drivers to adopt the desired speed. Without any intervention and without being caught and fined undesired behaviour like fast driving usually has positive consequences for drivers. Behaviour modifications by positive reinforcement of individual drivers have not yet been widely used in traffic. The authors describe a feedback system tested in Krefeld, Germany, which involves positive consequences for desired behaviour and explicitly refers to the regulation which is kept to or violated. Drivers who do not keep to the speed limit are not threatened with punishment but they are made aware of the possible consequences of their behaviour. Both display types, the combination of `thumb - 30 - thank you' and `30 - please' as well as the sign `child - 30 - please' led to a reduction of the mean speed of cars. The effect of the displays from the point of view of safety is higher than the reduction of the mean speed shows, as the proportion of very fast cars were markedly reduced, which can be seen in the distribution of speeds. The higher the speed at a road position in the baseline condition, the larger was the speed reduction. This result matches that found when speed-30-areas are imposed without additional measures: the speed reduction is higher when the baseline speed is higher.
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