In the Netherlands, the Sustainable Safety vision is an important guide in improving road safety. In this vision, a central principle is 'predictability'. This principle builds on the idea that the road design should conform to the expectations of road users in order to prevent errors that could lead to road crashes. To study the effect of a predictable road design on driver behaviour, we examined speed and lateral position at rural roads that varied in their predictability. These behaviours were examined in light of general safety effects and a more specific hypothesis thatuunderlies the predictability principle: does a predictable road design lead to more homogenous road user behaviour (and thus to more predictable and safer behaviour)?uThe results of this study showed that the more 'predictable' road designs induced more homogeneous lateral positions between vehicles, whereas speed distribution remained unchanged. The more 'predictable' roads also resulted in lower (and thus safer) mean speeds and lateral positions that were closer to the shoulder of the road and. Because of the potential safety effects of road design on behaviour, these effects should be examined as a whole, before implementation of the design. (Author/publisher).
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