Effectiveness Evaluation of the Safety Improvement of Sharp Horizontal Curves in Mountainous and Rolling Rural Roads

Document Type : Original Article

Authors
Hamid Reza Behnood 1
Soheil Saadatifard 2
1 Associate Professor, Department of Civil Engineering, Faculty of Technical and Engineering, Imam Khomeini International University, Qazvin, Iran.
2 M.Sc., Student, Department of Civil Engineering, Faculty of Technical and Engineering, Imam Khomeini International University, Qazvin, Iran.
10.22034/road.2025.474515.2314
Abstract
Horizontal curves are one of the most dangerous parts of the road. The main goal of this research is to investigate the effect of curve radius as the most important factor affecting the frequency of crashes. In this regard, the crash modification factor (CMF) will be obtained as a basic criterion in the analysis of crash prediction models for horizontal curves as a function of its radius. Improving the characteristics of horizontal curves, such as increasing the radius of the curve, can have an effect on reducing the number of crashes. In this research, the crashes at sharp curves for four-lane and two-lane suburban mountain and rolling roads in Qazvin province in the years 2014 to 2016 have been investigated. Negative binomial regression has been used to develop safety performance functions for improved and non-improved curves. Then, by weighting the observed and predicted crashes according to the overdispersion parameter, the expected crashes for improved and non-improved curves were obtained and by dividing them by the same value, the CMF coefficient was obtained. In two-lane roads, for radius values less than 150 meters, the value of the CMF function increases, and this means that reducing the radius has made the curve safer. The linear relationship in the four-line roadways shows the decrease of the CMF coefficient and the crash potential with the increase of the horizontal curve radius.
Keywords
Horizontal Curve
Crash Modification Factor
Crash Predictive Model
Negative Binomial
-Al-Marafi, M. N., & Somasundaraswaran, K. (2023). A review of the state-of-the-art methods in estimating crash modification factor (CMF). Transportation Research Interdisciplinary Perspectives, 20, 100839.
-Anna, V. B. K., & Chunchu, M. (2023). Determinants of speed variability on the horizontal curves of two-lane undivided rural highways passing through mountainous terrain. International Journal of Injury Control and Safety Promotion, 30(4), 652-665.
-Banihashemi, M. (2016). Effect of horizontal curves on urban arterial crashes. Accident Analysis & Prevention, 95, 20-26.
-Bonneson, J. A. (2000). Kinematic approach to horizontal curve transition design. Transportation Research Record, 1737(1), 1-8.
-Cafiso, S., Montella, A., D’Agostino, C., Mauriello, F. and Galante, F., 2021. Crash modification functions for pavement surface condition and geometric design indicators. Accident Analysis & Prevention, 149, p.105887.
-Carter, D., Srinivasan, R., Gross, F., & Council, F. (2012). Recommended protocols for developing crash modification factors. Final Report NCHRP, 2027(314).
-Choi, Y. H., Park, S. H., Ko. H., Kim, K. H., & Yun, I. (2018). Development of safety performance functions and crash modification factors for expressway ramps. KSCE Journal of Civil Engineering, 22, 804-812.
-Findley, D. J., Hummer, J. E., Rasdorf, W., Zegeer, C. V., & Fowler, T. J. (2012). Modeling the impact of spatial relationships on horizontal curve safety. Accident Analysis & Prevention, 45, 296-304.
-Fitzpatrick, K., Lord, D., & Park, B. J. (2010). Horizontal curve accident modification factor with consideration of driveway density on rural four-lane highways in Texas. Journal of Transportation Engineering, 136(9), 827-835.
-Geedipally, S.R., Pratt, M.P. and Lord, D., )2019(. Effects of geometry and pavement friction on horizontal curve crash frequency. Journal of Transportation Safety & Security, 11(2), 167-188.
-Gross, F., Persaud, B. N., & Lyon, C. (2010). A guide to developing quality crash modification factors (No. FHWA-SA-10-032). United States. Federal Highway Administration. Office of Safety.
-Harwood, D. W., Council, F. M., Hauer, E., Hughes, W. E., & Vogt, A. J. B. T. (2000). Prediction of the expected safety performance of rural two-lane highways (No. FHWA-RD-99-207, MRI 4584-09, Technical Report). United States. Federal Highway Administration.
-Hauer, E., Bonneson, J.A., Council, F., Srinivasan, R. and Zegeer, C., 2012. Crash modification factors: foundational issues. Transportation Research Record, 2279(1), 67-74.
-Ma, Q., Yang, H., Wang, Z., Xie, K. and Yang, D., 2020. Modeling crash risk of horizontal curves using large-scale auto-extracted roadway geometry data. Accident Analysis & Prevention, 144, 105669.
-National Research Council (US). Transportation Research Board. Task Force on Development of the Highway Safety Manual, & Transportation Officials. Joint Task Force on the Highway Safety Manual. (2010). Highway Safety Manual (Vol. 1). AASHTO.
-Wu, L., Lord, D., & Geedipally, S. R. (2017). Developing crash modification factors for horizontal curves on rural two-lane undivided highways using a cross-sectional study. Transportation Research Record, 2636(1), 53-61.