Reliability analysis of pedestrian crossing sight distance

The main objective of this study was to calculate the required sight distance corresponding to the various probabilities of failure by considering two methods of reliability analysis. This paper presents a probabilistic approach based on such random variables as major road vehicle speed, walking speed, pedestrian observation-reaction time, the length of the crossing unit, pedestrian setback from the nearest curb of the major road. A safety margin is defined as the difference between available and required sight distances. By using the first-order second moment (FOSM) method, relationships for the mean and standard deviation of the safety margin were developed. The advance first-order second-moment (AFOSM) was also used to find the supplied sight distance corresponding to reliability index. Comparison of two methods was done. Obtained results from the two methods were almost similar to a low coefficient of variation. Different design graphs were developed to calculate the required sight distance at a different coefficient of variation corresponding to the probability of failure and different vehicle design. Sensitivity analysis was performed to obtain the most sensitive variable to the pedestrian crossing sight distance. It was found that vehicle speed is more sensitive to required sight distance and perception-reaction time has least effect on supplied (required) sight distance. Application of these methods is presented with two examples. This probabilistic method is valuable in designing pedestrian crossing sight distance for any preferred reliability level.