POTENTIAL CONFLICTS

The traditional standard of thinking for engineering roadways is that trees are to be avoided. The main reason is to reduce the number of obstacles which are at the edge or within the right-ofway. Street trees and other vegetation can be are hazards to sight lines at intersections and private drives. They also are dangerous when motorists do collide with them often resulting in a severe or even fatal accident depending on the speed of the vehicle.

Additionally, the relationship between crashes and trees is not very well understood. It is difficult to prove that street trees prevent crashes from happening. It is important to understand driver behavior in connection with roadside features. It could be argued that adding more to the environment for a driver to pay attention to could increase the crash risk and rates.

One thesis study from 2017 by Maggie Harthoorn at the University of Nebraska-Lincoln concludes that there is a relationship between street trees and roadway safety. The study looked at crash severity in Des Moines, Iowa and ultimately determined that there is no significance between the density of street trees and frequency of the crash rates despite there being a relationship between street trees and roadway safety. A lot of this comes down to human error. However, there is a positive relationship between street trees and crash severity. This unfortunately means that street tress increases the risk of crashes being more severe. When planting street tress, location needs to be a top priority and receive additional consideration as to try and prevent the possibility of increased crashes.

Cost

Low to moderate cost depending on the implementation level. One planting can cost from roughly $250 - $600 including maintenance for the first three years. They are generally planted anywhere from four to eight feet from the curb.

Additional landscaping costs will also vary depending on the plantings (flowers and shrubs).