EVALUATING THE SAFETY RISK OF NARROW MEDIANS AND RESTRICTEDSIGHT DISTANCE

摘要

In British Columbia, many highways are located in mountainous terrain and the costs of highway construction inrnthese areas are high. One method of controlling construction costs is narrow medians but the safety consequences ofrnusing narrow medians were never determined. Recent research on safety in geometric design has focused onrnestablishing quantitative relationships between collisions and cross sectional elements using collision predictionrnmodels (CMPs) and collision modification factors (CMFs). In some situations, such as the use of narrow medians, itrnis difficult to find CMPs and CMFs that adequately describe the design scenario. In other instances, it is difficult tornmeasure the safety in terms of collision reduction because of a lack of data or difficulty isolating the impact of arnsingle design element on collision frequency. In these situations, reliability analysis can be used to evaluate the riskrnassociated with a particular design feature. In this paper, reliability analysis was completed on a series of horizontalrncurves with varying horizontal sight distance restrictions and the probability of being unable to stop within thernavailable sight distance was calculated. The results of the study found that narrow medians combined with tightrnhorizontal curves did not provide enough sight distance that vehicles would be expected to stop if an object was in arnvehicle's path. The analysis was applied to a case study of two constrained alignments in mountainous terrain ofrnBritish Columbia.