Urban trees and traffic safety: Considering the U.S. roadside policy and crash data

This paper begins with a helpful review of how the engineering standards and guidelines used in managing the interface between roads and trees have developed. In particular, it is noted that guidelines for rural roads and highways may be inappropriately influencing urban design without regard for the lost benefits when trees are removed or not planted in the first place. This study is an exploratory analysis seeking patterns of association when trees are implicated in roadside crashes and evaluating how those patterns might differ in an urban vs rural areas. Tree collisions are indeed a risk. They accounted for only 1.9% of all traffic accidents in the year studied (2002), but 46% of these crashes were severely injurious or fatal. When data on traffic accidents were broken out into urban vs rural, crashes were more frequent in rural areas, collisions with fixed objects like trees were more common in rural areas, and crashes in rural areas were generally more harmful (likely as a result of higher speeds in these areas). Because driving conditions in urban areas are quite different, more research is needed to serve as a basis for guidelines for trees along urban streets. This research can be used as a component of Context Sensitive Solutions, a national policy intended to better incorporate community values into transportation planning.