Abstract During design and construction of a new roadway or when considering the upgrading of an existing one, it is important to provide a free space alongside the roadway for errant vehicles to recover and stop without striking an obstacle. Recovering or stopping errant vehicles requires wide free spaces to provide enough time and space for desired maneuvers and for avoidance of roadside accidents. While there are obvious safety benefits for providing wider clear-zones, the construction cost of a wide clear-zone in a rock cut can be formidable since it involves excavating and removing large quantities of rock and earth. Good clear-zone design entails balancing the improved safety of wider clear-zones with the reduced cost of narrower ones. This work deals with one specific type of clear-zone problem—identifying the most cost-effective clear-zone width through rock cuts. Many roadside safety countermeasures (e.g., removing trees and installing guardrails) have relatively low costs in comparison to other construction costs (e.g., grading, paving, and building structures). Clear-zones in rock cuts, however, can be very expensive since removing additional volumes of rock involves heavy construction equipment, blasting, and removing materials from the site. If the safety of the roadway were not a consideration, a rock cut could be limited to the width required to accommodate the travel lanes, shoulders, and drainage features. Although the construction cost of such a roadway would be minimized, the expected societal cost of accidents in the rock cut would quickly erode these short-term construction savings. The objective of this study is to quantify the societal cost of rock face accidents in Iran, so that the costs and benefits associated with different clear-zone policies can be explicitly addressed during the preliminary design process. Malcolm in 1996 assessed safety and cost-effectiveness of clear-zones in Rock-cuts in northern Ontario, Canada (Malcolm, 1998). The existing alignment of the study segment is a two-lane undivided highway that passes through rock-cuts, in the province of Fars in Iran. The appropriate clear-zone width is selected based on the design speed and the design Average Daily Traffic (ADT). The U.S. Roadside Design Guide [AASHTO] recommends a clear- zone of 10 m from the outside edge of the lane on roadways with average annual daily traffic (AADT) of over 6 000 vehicles/day and a design speed greater than 120 km/hour (AASHTO, 2002).

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