Community and Regional Planning Program


First Advisor

Dan Piatkowski

Date of this Version



Harthoorn, Maggie. (2017). Influence of Street Trees on Roadway User Safety. Lincoln: University of Nebraska-Lincoln.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Community and Regional Planning, Major: Community and Regional Planning, Under the Supervision of Professor Daniel Piatkowski. Lincoln, Nebraska: November, 2017

Copyright (c) 2017 Maggie Harthoorn


This thesis aims to understand trends of trees in transportation planning and to determine if street trees have a negative or positive influence on crash frequency and severity. As roadways become more walkable and livable, they become safer. Street trees are a vital component of this trend. Planners must understand the impacts of trees on roadway user safety as they work to reduce crash risk. Although spatial analysis suggests there may be a negative relationship between trees and crash frequency, correlation models find a significant correlation between trees and crash severity, but no significant correlation between trees and crash frequency. Regression models of crash reports, tree inventory data, and other related variables in the city of Des Moines, Iowa, show that the presence of trees has a positive relationship on crash severity but no relationship on crash frequency. For every one unit increase in trees there is a 1.428 increase in predicted severe crashes, but an increase in trees does not result in any statistically significant influence on crash frequency. These findings are useful in gaining an understanding of tree influences on crash frequency and severity at the block group level, but further analysis of other variables is necessary for any further conclusions to occur.

Advisor: Daniel Piatkowski