A Procedure to Test the Safety Level of Road Design Elements

Since 1992, 'Sustainable Safety' has been the leading road safety concept in the Netherlands. The main objective of a sustainably safe road transport system is to reduce the number of traffic casualties to only a fraction of the current annual number. The most important ways to achieve this are to prevent latent errors in the traffic system as much as possible, and to let road safety depend as little as possible on individual road user decisions. The four main principles for road design are: 1. functionality; 2. homogeneity; 3. recognizability/predictability; 4. forgivingness. The fifth Sustainable Safety principle, 'State awareness' (by the road user), involves the ability to assess one's task capability to handle the driving task and has no direct effect on road design. The first principle, functionality of the traffic system, is important to ensure that the actual use of the roads is in accordance with the intended use. For this reason, each road or street may only have one function: flow, access or distribution. The second principle, homogeneity, is intended to avoid large differences in speed, direction, and mass by separating transport modes and, if that is not possible or desirable, by making motorized traffic drive slowly. The third principle should result in a design (of the road and its environment) which promotes the recognizability of the road categories, and therefore the predictability, of the traffic situations that may occur. In this way, undesirable traffic situations can be acknowledged and avoided in time. The fourth principle is intended to limit injury severity by a forgiving road environment. Each principle has been specified into a set of requirements for road design. To test these requirements, the Sustainable Safety Test was developed. The requirements can be tested during various design phases (from the planning phase to the reconstruction phase). In essence, the Sustainable Safety Test compares each indicator of a planned or existing situation with the test criteria. The result of the Sustainable Safety Test consists of calculated percentages that indicate which proportion of the road length (or which proportion of the intersections) meets the various sustainable safety requirements. Recently EuroRAP (European Road Assessment Programme) launched another type of test: the Road Protection Score (RPS). The RPS test focuses on a set of criteria, which specifically relate to the safety of a car driver; the Sustainable Safety Test also takes into account the safety of other road users. The present paper will discuss the differences and similarities between both tests. The Sustainable Safety Test was applied several times: in research projects (e.g. evaluation of zones with a 60km/h speed limit, evaluation of main roads in a city), and in several design stages of a planned light rail track in a medium-sized city. The RPS test was applied to national roads and to a share of the provincial roads. If a road (design) meets the sustainable safety requirements, and thus scores a high percentage on the Sustainable Safety Test, this does not automatically mean that from now on there will be no more crashes. Fulfilling the requirements means that the road design meets the most important safety conditions. The same applies to the criteria of the RPS test. How the requirements and criteria are linked to crash patterns and to crash types is a subject of research.