Self-explaining roads

As a means to a sustainable safe traffic environment the concept of Self-Explaining Roads (SER) has been developed. The SER concept advocates a traffic environment that elicits safe driving behaviour simply by its design. In order to support safe driving behaviour and appropriate speed choice, drivers should be enabled to recognise the type of road they are on. Therefore, it is important that the way people subjectively categorise these roads matches the function and use of roads. However, most Dutch roads do not display enough structure to allow for an effective utilisation of these SER design principles yet. Several studies indicate that road users are not able to distinguish roads according to official road categories.
So far, no studies have explicitly addressed the relationship between cognitive road classification and actual driving behaviour. The present study investigated to what extent cognitive road classification determines driving speed. Both a picture-sorting task and a driving simulator task were used to investigate the effects of design characteristics on cognitive road classification and driving behaviour. In both tasks, three road design conditions were involved: one consisted of a set of Current Roads, roads as they are in reality; one of a set of Self-Explaining Roads; and one of both Current Roads and Self-Explaining Roads. Each of the three different sets of roads consisted of eight exemplars of each of four road categories: motorways, motorroads, 80 km/h roads for fast traffic and 80 km/h roads for mixed traffic. The picture-sorting task showed that subjects categorised Self-Explaining Roads more in accordance with the official road category system than Current Roads. A more systematic application of road design elements results in a subjective road classification that is more in accordance with the official road category system.
Subjects did not only classify on the basis of road characteristics, but they also used the whole set of road environments, the context, they were part of. The driving simulator task showed that driving behaviour on motorroads with a SER design was more in accordance with driving behaviour as meant by the official road design. No clear-cut evidence was found for an effect of cognitive road classification as such on the level of driving speed. Yet, results showed that a more consistent road design within categories may lead to more homogenous driving speeds.