Effects of tree canopy on rural highway pavement condition, safety, and maintenance

"Phase I"--Technical Report Documentation Page.; "Prepared for: The Ohio Department of Transportation Office of Statewide Planning and Research"--Cover.; "Prepared in cooperation with the Ohio Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration."; "February 2017."; Includes bibliographical references (pages 64-74).; Final report.; Sponsored by: Ohio Department of Transportation, Office of Research and Development; State Job Number 135320An integral part of Ohio's roadscape is the canopy cover alongside and above the pavement. Roadside trees are valued for their natural beauty and because they provide shade, moderate temperature fluctuation, control evaporation, block air movement, catch rain and channel rain wash, and control local humidity. However, road managers tend to believe that trees cause accelerated moisture damage, poor density attainment, surface water pooling, and surface roughness in pavements. They infer these processes likely accelerate damage and reduce longevity of pavements, which leads to an undesirable increase in pavement maintenance and rehabilitation costs. A large body of published research confirms that trees control microclimate in urban settings, and that climatic environment is one of the factors affecting pavement deterioration. Similarly, tree canopy can negatively impact pavement surface condition, decreasing driver safety. However, these ideas are subjective to a large extent and yet to be scientifically explored through a dedicated study (especially in suburban/rural settings with seasonally cold climate such as in Ohio) of the multiple connections between trees and pavement degradation, road condition, and road safety. As a first step, this research study provides ODOT with a synthesis of existing practices from Ohio and some other states related to maintenance of roadside tree canopy (overtop and adjacent to roadways). Inconclusive evidence and conflicting information from surveys and the literature suggests an immediate need for a larger and focused study of tree canopy impacts on road pavement condition and driver safety. Consequently, this report concludes with a clear plan for designing and implementing such a study (Phase II). The most important contribution of such a detailed study will be a formal decision-making system that ODOT can use for objectively assessing the economic and environmental trade-offs of maintaining and/or cutting trees.