Beïnvloeding van snelheidsgedrag door nudging : vragenlijstonderzoek naar het effect van Dick Bruna-borden op geschatte rijsnelheid binnen de bebouwde kom.

Influencing speed behaviour by nudging : questionnaire study into the effect of Dick Bruna1 traffic signs on the estimated driving speeds in urban areas. Speed is an important risk factor in traffic. Measurements within urban areas on 30- and 50 km/hour roads show that the percentage of speeders on these roads is considerable. The traditional methods to influence driving speeds in the Netherlands are infrastructural measures, credible speed limits, public information and enforcement. The ultimate goal is to evoke safe driving speeds by realizing a logical and clear road layout in combination with safe and credible speed limits. The road and the physical environment of the road should elicit, as it were, safe and desired speed choice. Lately, there has also been considerable interest in additional methods that can help reduce high speeds. From an interest in measures that can have a positive influence on driving speed without drivers being aware of it (automatic influence on behaviour or 'nudging'), the metropolitan region Rotterdam the Hague asked SWOV the following question: 'Do drivers who have been exposed to Dick Bruna signs choose a lower speed than drivers who have not been exposed to images or to neutral images?' The Dick Bruna illustrations were chosen because they are well known among a large part of the population and are associated with children. This report presents a questionnaire study that was carried out as a first step in answering this question. In an experimental setup respondents were shown online photographs of 30- and 50km/h roads and were asked to estimate their own speed and the speed of others. For this study the following expectations were formulated: 1. We expect that (a) respondents report a lower preferred speed on roads where a Dick Bruna sign is placed than on the same roads without a sign, and that (b) respondents do not differ in preferred speed on roads with a neutral sign (for example advertising a soft drink) and the same roads without a sign. 2. We expect that (a) respondents expect others to drive at a lower speed on roads where a Dick Bruna sign is placed than on the same roads without a sign, and that (b) respondents do not expect others to drive at different speeds on roads with a neutral sign (for example advertising a soft drink) and the same roads without a sign. The number of respondents in the study was 1,021, their average age was 45.6 years, 50% were male and 50% were female, and their average annual mileage was just over 16,000 km. This representative group of Dutch drivers was selected by a specialized panel agency. The group was composed according to the composition of the population in the Netherlands in the age category 18 to 74 years-old. In this way we ensured that a representative group (young/old, male/female) assessed the photographs of roads and road signs. The respondents who were selected in this way were then randomly distributed over the different conditions of the study. The results support both expectations. Drivers estimate their own preferred speed and the speed of others to be about 4 km/hour lower when they see a Dick Bruna sign than in the same situation without a Dick Bruna sign. This effect is virtually the same for 30 and 50 km/h-roads. In road safety terms a speed reduction of 4 km/hour has a large effect: in real traffic such a reduction of the average speed on a road in an urban area would result in a 20% reduction of in crashes (Elvik, 2009). Drivers who see a Dick Bruna sign at the side of the road were also found to give a lower estimate of the preferred speed of themselves and of others than drivers who see a neutral sign at the roadside. The neutral sign did indeed appear to be virtually neutral in terms of the effect on driving speed. There was, however, a statistically significant difference between the own preferred speeds in the situations with a neutral sign and without a sign, but in absolute terms, this difference was small (0.4 km/hour). The main conclusion is that the results confirm the hypothesis that images at the roadside can be used to achieve a potential and substantial reduction of the driving speed by nudging or automatic influence on behaviour. It must, however, be noted that the results were obtained by a questionnaire study: self-report in an experimental context. For various reasons the results cannot be translated into practice directly. We therefore recommend to expand this study with roadside measurements.