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theses

Highway agencies worldwide remove roadside trees in the name of traffic safety. In 2017, the Georgia Department of Transportation (GDOT), the agency charged with managing state and federal highways in the US state of Georgia, began clear-cutting trees across highway property statewide, amounting to thousands of acres of cleared land. As justification, GDOT cited fatal traffic crashes with trees. However, since tree removal began in 2017, tree crash fatalities statewide have not significantly decreased. The American Association of State Highway and Transportation Officials (AASHTO) issues guidance for highway agencies to maintain clear zones adjacent to the roadbed, free of trees, to reduce the severity of run-off-the-road crashes. Some highway agencies, like GDOT, are clearing trees beyond the standard clear zone for road safety, creating friction between units of different disciplines. Other countries with better traffic safety records than the United States do not engage in large-scale roadside tree clearing. Figures in the Roadside Design Guide are based on decades-old studies with questionable results. The authors at the time knew of the shortcomings of their studies, but their commentary and qualifiers have been left out of the existing guidance.
In this dissertation, I quantified the extent of roadside tree removal along Interstate 16, from Macon to Savannah, using the United States Department of Agriculture (USDA) Farm Service Agency’s National Agricultural Imagery Project (NAIP) and Normalized Difference Vegetation Index (NDVI) differencing to assess greenness change between 2015 and 2021 imagery. I also collected pre- and post-treatment tree crash fatality data. I used semi-structured interviews with agency staff in the US and abroad to illuminate how perceptions of trees—either as safety hazards or as beneficial environmental assets— are considered by practitioners at highway agencies.
Results showed that 12.7 sq km of the corridor became less green, indicating tree removal in 27% of the I-16 corridor. Over 68% remained at the same level of greenness. About 2 sq km (4.9%) became greener. Results from interviews indicate that engineering leadership in the US and abroad understands roadside tree management as a nuanced issue. The benefits of trees are understood by most staff, but in the US, these benefits are sidelined by a focus on expediency and misperceptions about traffic safety. Maintenance staff in the US are motivated more by budgets or contracts than by research or federal guidance. An interdisciplinary staff structure, robust communication practices, and stronger environmental policy can improve highway agency collaboration in the US.

http://dissertations.umi.com/gsnb.rutgers:12407

Ph.D.

Includes bibliographical references

doi:10.7282/t3-17w2-8107

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