Assessment and Design Methodology for the Identification and Remediation of Rock Snagging Hazards on Road Cuttings – A Case Study from the Hervey Range Road Safety Upgrade Program Project

Hervey Range Developmental Road (83A) is a two-lane, two-way single carriageway rural road connecting Townsville to Hervey Range and outer suburban residential areas such as Alice River and Rangewood. As part of a safety upgrade program along Hervey Range Road, identification of rock snagging locations and design of value for money smoothing solutions were required to be undertaken due to the need for widening of the sealed road alignment and the proximity of the existing rock cuttings relative to the road. An assessment methodology for identifying what constitutes a rock snagging hazard in a quantitative sense is either not well defined or inconsistent when considering published literature (such as various state road authority specifications and other Australian road design guidelines). In light of this, a definition of a rock snagging hazard was developed for the project and can be qualitatively defined as a rough, sharp or jagged rock protrusion or depression which has the potential to constitute a hazard to vehicular navigation. This paper describes the qualitative and quantitative assessment criteria and design methodology that has been adopted to address the risks associated with rock snagging hazards on irregular and often jagged road cuttings that are close to the edge of the road using the Hervey Range Road Safety Upgrade Program project as a case study. The assessment of rock snagging hazards without the necessary budget for detailed field assessment and mapping, as well as fit for purpose detailed survey, can complicate the ability to provide cost effective remedial solutions to this type of problem. Two-dimensional analysis of survey can often prove problematic with regards to identification of the hazards. This paper discusses how interrogation of the available information through rendered three-dimensional survey assessment in conjunction with digital video recorder (DVR) footage and still imagery, as well as use of conventional two-dimensional analysis of cross-sections and long- sections, can be used to provide value for money smoothing solutions. An innovative design methodology incorporating the vertical extent of treatment on slopes to reduce the risk of safety in construction as well as reducing the construction costs was also implemented as part of the project.