Reliability of sight distance at stop-control intersections Available to Purchase

The American Association of State Highway and Transportation Officials presents guidelines for intersection sight distance (ISD) based on extreme values of the component design variables such as speed and time gap. The guidelines for a stopped vehicle at a stop-control intersection on a minor road assume that the component design variables are deterministic. This paper presents a reliability method that considers the design variables as random. The method uses the means and variances of the probability distributions of the random variables and accounts for their correlations. A safety margin is defined as the difference between available and required ISD. Relationships for the mean and standard deviation of the safety margin are developed based on first-order second-moment analysis. The proposed method is useful for ISD design of a new intersection or redesign of an existing intersection for a desired reliability level. For single-unit trucks, the obstruction clearances from the minor- and major-road pavement edges are approximately 10% higher than those for passenger cars. The proposed method should be of interest to highway engineers involved in road safety and management.