System reliability as a surrogate measure of safety for horizontal curves: methodology and case studies

Reliability analysis has been advocated to account for the uncertainty in geometric design and to evaluate the risk associated with various design options. Most of the previous studies using reliability-analysis in highway design evaluated only one-mode of noncompliance. This study assesses the performance of horizontal curves using a system of multi-modal noncompliance (insufficient sight distance, vehicle skidding, and vehicle rollover). Five case studies of a highway in British Columbia are considered. Two approaches were used: (1) second-order reliability-bounds with FORM analysis (First-Order Reliability Method), (2) Monte-Carlo Simulation (MCS). A calibrated design chart that accommodates heavy-trucks on horizontal-curves with sharp-radii is provided. The results show that the differences in the system probability of noncompliance between one-mode and system of multi-modes of noncompliance are more pronounced for heavy-trucks. Results also show that the probability of noncompliance associated with vehicle rollover is significantly affected by the stability-ratio compared to height-ratio and roll-rate.

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