Investigation of the Effects of Concave and Convex Conditions of Steel Guardrails Installed Inside Curves on the Safety Parameters According to the EN 1317 Standard Using Finite Element Analysis

Steel guardrail systems play a critical role in reducing injury severity during run-off-road crashes, especially on horizontal curves where accident rates are high. However, validation procedures defined in the EN 1317 standard are predominantly based on crash tests performed on straight road sections, and the influence of curved geometries is not sufficiently considered. This study numerically examines the effects of concave and convex horizontal curves on the safety performance of steel guardrails using finite element analysis (FEA). An EN 1317-compliant H1W4-A steel guardrail system was developed and validated under TB11 crash test conditions using LS-DYNA. The validated model was subsequently applied to concave and convex curve configurations with radii between 30 m and 210 m, resulting in a total of 14 numerical crash simulations. Key occupant safety parameters, namely the Acceleration Severity Index (ASI) and Theoretical Head Impact Velocity (THIV), together with structural performance measures such as working width (W) and exit angle (α), were systematically evaluated and compared with straight-road reference conditions. The results indicate that concave guardrails generally exhibit reduced impact severity, reflected by lower ASI and THIV values, compared to straight-road cases. In contrast, convex guardrails lead to higher and more critical safety indices, particularly at smaller radii. Although most configurations remain within EN 1317 limits, the R30 concave case exceeds allowable exit angle and working width thresholds. These findings highlight the necessity of incorporating road curvature effects into guardrail safety assessments.