Reliability-Based Analysis of Sight Distance for Highway Safety in Hilly Terrain

The main objectives of the present study are to calculate the reliability index as a function of sight distance and corresponding provide some possible geometrical improvements. Therefore, 38 curves with varying geometry located along the two-lane rural hilly terrain were selected as a study area. The speed data were collected using a performance box (V-box) for car and heavy commercial vehicles (HCV). From that, at three curve points, vehicle speed was extracted. The first-order reliability method (FORM) is used to calculate the reliability index of the curve. The results revealed that curve radius and available sight distance are positively related to the reliability index. In contrast, the mean speed of cars and HCV has a negative relationship. The car has lower reliability as compared to HCV. Further, a curve having lower reliability required a higher setback distance and vice-versa. Similarly, a curve with a radius less than 150 m requires more setback distance than a curve having greater than 150m curve radius. The study's outcome will be useful for the highway authority to increase the operational efficiency and safety of the drivers/vehicle.