A Landslide Hazard Rating System for Colorado Highways

Landslides pose hazards along many stretches of Colorado highways. To assist in quantifying hazards and risks from known, existing landslides and to help prioritize their importance, the Colorado Landslide Hazard Rating System (CLHRS) was developed as a companion to the existing rockfall rating system used by CDOT. A preliminary version of the CLHRS was generated based on a review of the current body of technical literature regarding the factors that contribute to landslide hazard, consequence, and risk. It consisted of eleven Hazard Factors and eight Consequence Factors to calculate an overall risk score. The preliminary CLHRS was used to evaluate 69 landslides distributed throughout western Colorado. The resulting scoring distributions were then subjected to a suite of statistical analyses in order to identify the factors that possessed the greatest statistical merit. The statistical screening led to a final functional version of the CLHRS consisting of six Hazard Factors (geology, vegetative cover, slope aspect, surface water influence, failure frequency, and slope angle) and six Consequence Factors (depth to slide plane, length of highway affected, average daily traffic, detour options, worst-case scenario detour time, and annual maintenance cost). The CLHRS total risk scores clearly identify a subset of the landslides with both highest hazard characteristics and potential consequences.