Comparison between qualitative and quantitative rockfall risk methods for a hazardous road stretch

In order to compare rockfall risk values characterizing road sections affected by several rockfalls, two procedures have been used: the modified Colorado Rockfall Hazard Rating System (mCRHRS) and the ROckfall risk MAnagement (RO.MA.) method. The first one is a qualitative method mainly based on a heuristic assessment and the second is a quantitative approach taking into account the occurrence probability of severe negative events. Even though the qualitative approach is not consistent with the definition of risk used in the quantitative procedure, we proved that mCRHRS ratings are comparable with risk values, expressed as probability of death of at least one occupant of a vehicle (fatal accident) exposed to the rockfall hazard per year.