Trees in Hazardous Locations: Appendix 15

Some Tree Crashes Are Not Related to Trees

Locations have been identified, by some states, that developed tree crash concentrations even though there were wide clear zones. These locations were identified by looking at the frequency of tree crashes. However, once investigations were completed, it was apparent that the problems were not primarily related to the location of the roadside trees.

One case, on a rural secondary road in North Carolina, involved a curve with reverse superelevation. Vehicles were running of the road to the right, over correcting and crossing the highway and striking the trees on the opposite shoulder. In this case, the trees were approximately 15 feet from the travel lane, placing the trees more than 25 feet from the travel lane from which the vehicles were departing before striking the trees.

Another case, in Florida, involved a relatively straight highway with an intersection located just over the crest of a small hill. This intersection did not have left turn lanes. As vehicles approached the intersection, the hill was just high enough to shield the view of left turning vehicles from vehicles approaching in the same direction. Vehicles were running off the road and striking trees more than 30 feet from the travel lane. There are two possible strategies that may be used, which do not affect the trees: lower the crest of the hill to eliminate the site restriction, or add a left turn lane to remove the left-turning vehicles from the through lanes. The latter of the two has proven to be effective in several locations (Exhibit 15-1).