New Geometric Design Consistency Model Based on Operating Speed Profiles for Road Safety Evaluation

In order to reduce road fatalities as maximum as possible, this paper presents a new methodology to evaluate road safety in both design and redesign stages of two-lane rural highways. This methodology is based on the evaluation of road geometric design consistency, determining one value which will be a surrogate measure of the safety level of a two-lane rural road segment. The consistency model presented in this paper is based on the consideration of continuous operating speed profiles. The models used for their construction have been obtained by using an innovative global positioning system (GPS)-data collecting method, based on continuous operating speed profiles recorded from individual drivers. This new methodology allowed the researchers to observe the actual behavior of drivers and to develop more accurate operating speed models than those which are based on spot-speed data collection. That means a more accurate approximation to the real phenomenon, and thus a better consistency measurement. Operating speed profiles were built for 33 Spanish two-lane rural road segments, and several consistency measurements based on the global and local operating speed were checked. The final consistency model takes into account not only the global dispersion of the operating speed, but also some indexes that consider both local speed decelerations and speeds over posted speeds. For the development of the consistency model, the crash frequency for all sites was considered, obtaining a model directly related to safety. This allows estimating the number of crashes of a road segment by means of the calculation of its geometric design consistency. Consequently, the present consistency evaluation method becomes an innovative tool that can be used as a surrogate measure to estimate road safety of a road segment even before its construction.