Speed is an inherent characteristic of mobility and a hazard to safety. Several approaches exist of how to manage speed. In the Netherlands, the emphasis has mainly been on harm minimisation during the last decades, due to the implementation of the Sustainable Safety vision. Speed management remains a core issue in this vision, by means of an integral approach of applying speed management measures. Setting a credible speed limit is one of the important issues here. A few years ago, a number of Dutch regional authorities asked for assistance in developing a decision support system for speed management as a basis for their traffic safety policy. In their opinion, speed management is of growing importance to improving road safety even further. Particularly the low casualty numbers present decision makers at the regional and local level a difficult job when they have to decide where and when to take action. Furthermore, some decision makers have the general question where they have a speeding or credibility problem and what can be an effective solution for that location. These issues were merged into a set of algorithms on safe speeds and credible speed limits (SaCredSpeed) that could be used in a decision support instrument for all types of roads. The SaCredSpeed algorithm uses input data of road design and image, and traffic characteristics of stretches of roads in order to calculate a safe speed and speed limit for that particular situation. This means that, depending on the legal traffic situation and further road design details, safe speed limits are defined. The safe speed is related to the real speed (V90 as a default) if this data is available. The SaCredSpeed algorithm can then check the credibility of the speed limit (current or ideal) and the enforcement situation (optional). Depending on the fit between the results of all these assessments, SaCredSpeed offers suggestions for adaptations. These can consist of a) speed limit adaptations, b) road design adaptations or c) additional adaptations in enforcement. These suggestions can also take into account the road network function, the condition of the adjacent roads, the traffic volume, and the priorities the decision maker wants to set. The first draft of the SaCredSpeed algorithm was tested in a number of regions in the Netherlands. The results from the safe speeds and credible speed limit assessments are discussed, as well as the SaCredSpeed suggestions for improving the situation. The paper will conclude with suggestions for further steps to take. (Author/publisher)
Abstract