Safety and cost-effectiveness of clear zones in Iran

Abstract

This paper examines different clear-zone improvement alternatives in rock cuts, and compares the likely effect on safety and construction costs. Where a roadway passes through rock cuts, the construction cost of providing the clear zone is very high. This paper is based on research that demonstrates a method for selecting the appropriate clear zone in rural two-lane highways in Iran based on the site and traffic conditions expected at the site. A method is described for determining the rock-cut width that best balances the cost of construction with the improvements in safety that would result from a wider clear zone in the rock cut. The objective of this study is to quantify the societal cost of rock-face accidents, so that the costs and benefits associated with different clear-zone policies can be explicitly addressed during the preliminary design process. This study shows that the need for extra clear-zone width in steep and bendy routes (specially with external curves of less than 195 m radius) is more critical than that for straight and level ones. The existence of external horizontal curves simultaneously with severe longitudinal slopes increases the probability of vehicles' encroachment by as much as eight times in comparison with straight and level routes. An interesting point to note is that, by providing wider lanes, the need for extra clear-zone width is reduced dramatically.