Predictable road user behaviour by a recognizable road design; a theoretical and practical exploration `Predictability' is an important principle for achieving a sustainably safe road traffic. This means that the road design must be so recognizable for the road user that he can know what to expect on different roads, and how he is expected to behave at any given moment. The result should be a more uniform, and therefore more predictable, behaviour. This report is an exploratory study in preparation of further studies of recognizable road design and its influence on the predictability of road user behaviour. The report consists of an exploration of the theory behind terms such as 'recognizability' and 'predictability' and their mutual relation, as well as an exploration of the practical situation: What is being done nowadays to improve the recognizability of roads, and what knowledge is already available? This knowledge needs to be taken into account in future research into elements that play a role in the predictability principle. The theoretical exploration was carried out with the help of mainly cognitive-psychological literature. Knowledge about predictability and recognizability is also available from studies of 'self-explaining roads', and from fieldwork on the behavioural effects of various road features. We carried out an inventory of the practical situation among various road authorities who at this moment are occupied with making road types more recognizable. Recognizability is based on the fact that people categorize their observations. This categorizing takes place at different levels of detail, it is flexible, and dependent on context. The required level of detail to categorize Sustainable Safety road types 'correctly' appears to be rather wide. This leads to the question whether the average road user has sufficient knowledge to recognize these roads, or whether additional knowledge is necessary, for example by including information about Sustainable Safety road categories in the driver training. The flexibility with which road users categorize roads raises the question which elements are crucial for recognizing road categories as they are intended in Sustainable Safety. These crucial elements are much more obvious for motorways (national through roads) than for 80 km/hour roads, (rural distributor roads). Seeing the dependence on context, the road surroundings also play a role in categorization by road users. This gives rise to the question if the Guideline Essential Recognizability Characteristics, which limits road user categorizing to recognizing road marking patterns, is sufficient to recognize roads as is intended in Sustainable Safety. This question gets extra emphasis because there is a great deal of variety in the implementation of this guideline. Research has shown that people find it more difficult to categorize if there is a large variety (too little uniformity) within categories and if the differences between categories are too small.
Samenvatting