Development of a global inertial consistency model to assess road safety on Spanish two-lane rural roads

The most important factors for road crash occurrence are infrastructure, vehicle, and human factors. In fact, infrastructure and its interaction with human factor have been thoroughly studied in recent years through geometric design consistency, which can be defined as how drivers' expectations and road behavior relate. Global consistency models were calibrated in the last decade to assess road safety on an entire homogeneous road segment. However, none of them include the underlying consistency phenomenon in their formulation. Recently, a new model was developed based on the difference between the inertial operating speed profile, which represents drivers' expectancies, and the operating speed profile, which represents road behavior. While the operating speed represents the estimated operating speed for every location along the road, the inertial operating speed aggregates for every station the operating speed effect along some distance already covered by drivers. The authors hypothesized that this 'aggregation effect' was connected to drivers' expectancies, which proved to be true based on the best model fitted. However, the exact distance (or time) that should be considered to estimate the inertial operating speed still remains unknown. This paper aims to complete this model, analyzing how the inertial operating speed varies depending on different distances and periods of time. This impact is measured considering the reliability of the corresponding consistency model. The paper also covers how the inertial operating speed should be determined along the final distance or time. For this, a total of 184 homogeneous road segments along 650 km in Spain were used.