ERASER is an acronym of “Evaluation to Realise a common Approach to Self-explaining European Roads”. This report is part of the ERASER project and serves as input for subsequent work-packages (WPs) within ERASER: It guides research in WP 2 during which road user pilots will be conducted. Based on this report, prototypical locations and design alternatives will be selected. Furthermore, it provides input for WP 3 which aims at developing a decision support tool for road authorities. This decision support tool is to provide road authorities with the necessary background to develop and implement self-explaining road (SER) categories. It will also incorporate a model to infer safe and credible speed limits. A feasibility check with road authority target groups to be conducted in WP 4 will ensure that this tool is accepted by the road authorities. Self-explaining roads were developed to increase inherent road safety by taking into account the nature of human perception and information processing. However, to increase road safety, self-explaining roads per se are not enough. Additionally, the entire road categorization has to be self-explaining. With traditional road categorization being the result of historical developments and sometimes dating back to the time when traffic safety was no major concern, this will not always be the case. In order to allow a common and modern state-of-the-art approach of self-explaining road categorization to be developed in Europe, the current practice of road categorization must be reviewed and compared with respect to their self-explaining properties. To achieve this aim, the report is structured into different parts. First of all, the background of road categorization is described in the first chapter of the report. This is followed by a second chapter which summarizes how road categorization impacts road design. In chapter 4, a definition of self-explaining roads is given. We adopted the definition of Theeuwes and Godthelp: “Traffic systems having self-explaining properties are designed in such a way that they are in line with the expectations of the road users. The [...] "Self-Explaining Road" (SER) is a traffic environment which elicits safe behaviour simply by its design.”(Theeuwes & Godthelp, 1995, p. 217) Because of the relationship of the SER approach and other approaches, chapter 5 is dedicated to explaining commonalities and differences between these approaches. In order to understand how a road can be made self-explaining psychological concepts are introduced in chapter 6. In addition, a paragraph is exclusively dedicated to influencing speed behaviour. After having explained SER principles for single roads, chapter 7 explains how an entire road network is made self-explaining. The crucial aspect is that road users correctly perceive the road category they are driving on and the behaviour expected from them on this category. Two principles were identified which support this aspect: * homogeneity within and * heterogeneity between road categories. However, in order to decide whether these principles are met, criteria to do so were identified in chapter 8. In addition a methodology is proposed how these criteria can be applied in a practical evaluation of the SER quality of a given road and road network. Before applying the first step of the methodology in chapters 10 and 11, an overview of the current practice of European road classifications is given in chapter 9. It was found that very few countries (The Netherlands, Denmark, Germany) actually apply or are developing SER approaches to road categorization. However, despite being largely in line with SER principles there are still weaknesses to be found. Whether such weaknesses in SER design affect behaviour will prototypically be tested in WP 2 of the ERASER project. Based on the preceding chapters an attempt was made to develop and introduce an ideal self-explaining road categorisation. This ideal can serve as basis for the evaluation of existing approaches but can also be used to develop a coherent SER classification for Europe. It is concluded that road categorizations differ widely in Europe and that only few countries are implementing or developing categorizations following SER standards. However, even those are at a starting point with none fully meeting SER criteria. It is thus concluded that additional empirical validations have to be performed in order to draw final conclusions. These empirical steps mainly have to deal with the question of whether designs which can formally be distinguished are also distinguishable by the road users — which is a prerequisite for a road categorization to become self-explaining. (Author/publisher)
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