The Nordic Explanatory Model

by Belinda la Cour Lund and Puk Kristine Andersson

Executive summary


When we as traffic engineers and planners try to understand road user behavior, we encounter challenges that are influenced by our traditional way of thinking, where we automatically assume that the road user is aware of his/her actions. In relation to an accident, this means that the road user - as a starting point - always has full legal responsibility for the accident consequences that may be caused by the road user's actions. Thus, the focus is usually on the road user and his/her inability. It is only in rare cases that the "system owner" is legally responsible. The "system owner" refers to the road authority, which is responsible for the design, construction, maintenance, etc. of the road, or the vehicle manufacturer, which has developed and produced the vehicle.

In the Nordic Explanatory Model , the focus is on making the road system more user-friendly and adapting the road system to the conditions of road users. In this paper, the focus is only on road users as drivers of motor vehicles.



The Nordic Explanation Model was developed in the years 2004-2014 as a collaborative project under the Nordic Road Geometry Group. The model has been reported in a large number of individual reports, memos, articles and case studies (see reference list). The Danish Road Directorate has asked Trafitec to prepare an easily understandable and practical summary of the entire project. The summary results in this handbook. The handbook is thus, as a starting point, based on already existing and prepared literature.

The handbook is aimed at traffic engineers and planners in the practical work of improving traffic conditions and road safety.


The Nordic Explanatory Model

To understand why a road accident occurs, it is necessary to know how we function as humans and to understand the actions of road users.

In general, traffic is considered as a system between road user, vehicle and road. Improving road safety requires better interaction between the three. The Nordic Explanatory Model is intended as a practical analytical tool that can be used to gain a deeper understanding of how we function in traffic and how our actions are affected by road design and the traffic environment. It is precisely the understanding of road users' actions that provides the best basis for identifying why different types of problems occur on the road network.

Whereas other models are often more road element-oriented and focus on more isolated and road geometric views, the Nordic Explanatory Model is a holistic model. A holistic model that, based on road user behavior, including physical and mental capacity, provides knowledge and understanding of how to design the road network in the best possible way.

If an experienced road user, despite normal caution, makes a mistake that results in an accident, the cause of the accident is usually sought in a broken or deficient interaction between the road user, vehicle and road. However, as it is not really possible to "re-design" the road user, the Nordic Explanatory Model focuses instead on changing the vehicle, the road and/or the traffic environment in such a way that the three factors are better adapted to the road user's conditions, including physical and mental skills. In this way, the real responsibility is placed on the "system owner" - i.e. the road authority.

Based on existing knowledge of road users' physical and mental capabilities, the Nordic Explanatory Model formulates some general principles for road user behavior. The development of the model has taken place in several steps. First, a number of basic characteristics of human behavior were described. This led to the formulation of some general principles of road user behavior. The principles were then used as a tool to analyze and explain some very specific problem areas in traffic. Thus, the model was used to try to predict the course of events in traffic. The predictions were then confirmed or rejected on the basis of empirical studies, such as traffic observations. If the predictions were rejected, the model was adjusted. In this way, the applicability of the model was tested several times and thus made operational.

According to the model, the general requirements for road design can be summarized by the principles of self-explanatory road design. The idea of the self-explanatory road is to have a limited number of road types with an easily recognizable design, thus giving road users correct expectations about traffic conditions, expected driving speed, the type of road users to which the road design is addressed, etc. An important element in the idea of the self-explanatory road is that expectations and behavior should, as far as possible, be based on natural information, such as the width, course and surroundings of the road, thereby reducing the need for symbolic information in the form of signs and other markings. When using symbolic information, it is important that it supports and reinforces the natural information.

The recognizability of the immediate overall perception of the road and the traffic environment is a fundamental prerequisite for the road user to have precise and correct expectations of the road, both in terms of the design of the road and the traffic situations that the road user must be prepared to encounter. The explanatory model is a tool - a way of thinking - for use in the development process that can lead to the realization of the self-explanatory road


Contents of the handbook

As a basis for the development of the principles of the Nordic Explanatory Model, an extensive literature study has been carried out on a number of important and decisive factors related to road user behavior. Chapter 2 contains a brief description of the most important factors, including road users' assessment of speed and distance, inattention and distraction, understanding and interpretation of information, etc.

Based on a literature study, behavioral theories, inspections and recordings of road user behavior in different traffic situations, five basic ideas are presented. Together, the five basic ideas aim to provide a better understanding of how we function as drivers - and why we act in certain ways when we are in traffic. The basic ideas are the core of the Nordic Explanatory Model and are described in Chapter 3 of the handbook.

Chapter 4 provides a brief summary of the model and its conclusions.

Based on the principles of the Nordic Explanatory Model, Trafitec has prepared four cases describing concrete examples of how the model can be used in practice. The examples are contained in Chapters 5, 6, 7, 8 and 9. All four cases focus on problems related to road works. In each case, the specific problem is described, the marking is reviewed and an assessment is made of why the problem occurs. Finally, suggestions are made as to what can be done to improve the situation.

Chapter 10 contains a list of references used in the preparation of Chapters 2, 3 and 4 of the Handbook.

Unless otherwise stated, photos and other figures in the handbook are part of the underlying references.

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