In the Netherlands, the Sustainable Safety vision is an important guide in improving road safety. It is considered that the road environment shouldconform to the expectations of road users in order to prevent errors thatcould lead to road crashes. These expectations are based on the characteristics of road types. The following types of roads are distinguished: access roads (30 or 60 km/h, vulnerable road users and agricultural vehicles possible, large amount of junctions), distributor roads (50 or 80 km/h, vulnerable road users separated from motorised traffic, no agricultural vehicles preferred, fewer junctions), and flow roads (100/120 km/h, no slow traffic, split-level junctions). Distinction of these road types and self-explaining characteristics are requirements for recognizable roads. To elaborate the predictability principle, 'essential recognition characteristics' (ERCs) have been defined. They consist of unique pattern of edge markings and lane separators per road type. Implementation of these ERCs has been started last years, especially on rural roads. Although there were good reasons for these ERCs to be specified, there was little knowledge about the effects on road user behaviour and road user expectations. To find out, SWOV examined these topics in a photo-categorisation study and a driving simulator study. In the first study, the distinctiveness and self-explaining characteristics of the different rural road types (15 photographs per roadtype) in various design options (ERC design and mix of ERC and traditional design) were investigated: The study showed that road users had most problems with distinguishing the distributor roads from the flow roads. Possible explanations for this finding were that these roads differ particularly on edge markings (in the ERC-condition), which is a characteristic road users pay insufficient attention to. The study also gave an indication of other road/environmental characteristics on which drivers pay attention byformulating expectations. The red cycle lanes along access roads appearedto be both distinguishable (access roads) and self-explaining (vulnerableroad users). In the second study, the effects of different design types (traditional design, ERC-design, ideal Sustainable Safety design) on road user behaviour (speed and lateral position) were examined. These behaviourswere examined in the light of general safety effects and a more specific hypothesis that underlies the predictability principle: does a recognizable road design lead to more homogeneous road user behaviour (and thus to more predictable and safer behaviour)? The study showed that the road designitself has a strong effect on driving behaviour: more physical lane separation, for instance induced slower driving, and lateral position shifted towards the shoulder of the road. The study showed also an effect on more homogeneous lateral positions between vehicles, but not in speed. From bothstudies, it is concluded that the new road design with ERCs provides a good basis for the distinction of different road types and safer road behaviour. The distinctiveness may, however, be improved further by a higher level of uniformity of road design per road type. Safer behaviour may particularly be improved by examining more carefully the specific combination of road design elements of each road type. For the covering abstract see ITRDE137145.
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