unoccupied car could be significant, and the consequences of impacting a person would be severe (Figure 10). These consequences are combined with the likelihood of failure and impact to determine the risk rating. Figure 10. The consequences of a tree falling on an unoccupied parked car are considered significant. If the car were occupied, the consequences would be considered severe. Tree Risk Rating A risk rating matrix (Matrix 2) is a means of combining ratings of likelihood and consequence factors to determine a level or rating of risk. The matrix approach was selected for use in this guide because of its broad acceptance, ease of use, and effective application for rating tree risk. This matrix was designed specifically for the evaluation of risk posed by tree failures. The limitations associated with using a matrix include the inherent subjectivity and uncertainty associated with the selection of both the likelihood and consequence factors, and the lack of comparability to other types of risk assessed using other means. In the tree risk assessment matrix, four terms are used to define levels of risk: extreme, high, moderate, and low. These risk ratings are used to com40