Recognizability of category transitions in infrastructural design : literature study of the guidelines and knowledge concerning category transitions, particularly those on intersections.

The recognizability of roads, the predictability of their course and road user behaviour is an important Sustainable Safety principle. Road users need to know which driving behaviour they are expected to show and what they can expect of other road users. The required driving behaviour and the correct expectations can only be elicited when the road environment is in accordance and has a recognizable layout. In SWOV's 2003-2006 Research Programme, the study of recognizable design was mainly aimed at road sections. The 2007-2010 Research Programme has a stronger focus on intersections, because this is where relatively many crashes occur. In addition, the driving task is relatively complex on intersections: modes of transport that are often separated on road sections meet again at intersections, either temporarily or not. At intersections, road users therefore will require some time to adjust their expectations about other road users, but also about the new road section they will enter after having crossed the intersection. An important intersection characteristic is that they pre-eminently are locations where transitions are situated. An important type of transition is that between different road categories. In the advanced version of Sustainable Safety, study of the recognizability of this specific situation at intersections is qualified as interesting. At a more detailed level, however, intersections have other types of transitions that are possibly relevant for road safety: transitions that ask the road users for a behavioural change (e.g. a transition between an 80 km/h and a 50 km/h distributor road), transitions between functionalities (from flowing to exchanging of traffic and back to flowing), but also transitions in the road image that need not have any meaning for the road user. This literature study has looked at what is known about the design of transitions at intersections, and about the design in relation with the recognizability of transitions. This report may be accessed by Internet users at http://www.swov.nl/rapport/R-2008-09.pdf