Updating French formulas for operating speeds on horizontal curves of rural two-lane highways

The knowledge of operating speeds is of a major interest in highway engineering. In France, formulas expressing V85 (the 85th percentile of the speed distribution of free-moving cars) as a function of some geometric characteristics have been established 20 years ago, and are still widely used. A study has been undertaken to update these formulas for horizontal curves. Speed and geometry data have been collected on 49 bends with various characteristics on flat terrain by dry weather. The paper mainly deals with the geometry and speed measurements, the data analysis, and the findings of this study, before some comments.