Relationship between predicted speed reduction on horizontal curves and safety on two-lane rural roads in Spain Oña López, Juan José De Garach Morcillo, Laura Calvo Poyo, Francisco Javier García Muñoz, Teresa María Consistency Horizontal curves Poisson distribution According to different studies, speed reduction is considered one of the major factors in contributing road safety. For that reason, several guidelines have been recommended for maximum desirable speed reductions from tangents to horizontal curves and for maximum differentials between design and operating speeds on horizontal curves. The Interactive Highway Safety Design Model (IHSDM) Design Consistency Module presents an analysis of the relationship between speed reduction and crashes for horizontal curves on U.S. two-lane rural highways. This paper presents the relationship between speed reduction and crashes for horizontal curves on Spanish two-lane rural roads. A model for using regression analysis to predict crashes is presented. Exposure, curve length (CL), and difference in 85th-percentile speeds (δV85) between successive tangents and horizontal curves, as well as between successive curves, are used. The model's coefficients were different from the ones obtained for U.S. highways, although the values of the goodness-of-fit criteria were similar. In addition, the relationship between crashes and different speeds is analyzed, taking the difference in speed as a speed differential not exceeded by 85% of the drivers traveling under free-flow conditions (δ85V), instead of considering it as δV85. The two models (δV85 versus δ85V) give very similar results. 2024-01-19T13:28:16Z 2024-01-19T13:28:16Z 2014 journal article Published version: Juan de Oña, Laura Garach, Francisco Calvo and Teresa García Muñoz (2014) Relationship between Predicted Speed Reduction on Horizontal Curves and Safety on Two-Lane Rural Roads in Spain. Journal of Transportation Engineering, 140(3), March 2014: 04013015. https://hdl.handle.net/10481/86979 10.1061/(ASCE)TE.1943- 5436.0000624 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional American Society of Civil Engineers