3. PROACTIVE MANAGEMENT
Tree and utility management practices are generally reserved for rural areas and are largely reactive, in that, the safety practitioner has to manage a preexisting concern. Since no known States are intentionally introducing trees that mature to significant diameters into the clear zones of high speed rural routes, few—if any—standards governing the practice exist.36
The lower speed urban setting is much different. Trees, hardscape, and utility poles are routinely placed in relatively close proximity to vehicles. There are a number of reasons for this:
- Aesthetics– A city's identity is closely associated with the aesthetic presented. To many travelers, it's the first indication of the community's character that they will encounter.37
- Health– Studies suggest that urban vegetation may be associated with increased levels of physical activity38 and decreased levels of depression.39
- Environment– Trees improve air quality through temperature reduction, air pollution removal, reduced ultraviolet radiation, and carbon storage.40 They improve water quality by detaining and filtering surface run-off, and releasing it back into the atmosphere. Trees beyond the roadside clear zone are also vital to the health of pollinators such as bees, birds, bats.41
Urban landscaping and forestry are an increasingly noticeable element of urban design, and the benefits they are believed to provide maintain that prominence. Therefore, the design process must balance their benefits with the necessity for roadside safety.42
36 California Department of Transportation, Trees and Highway Safety, (Sacramento, CA: March 18, 2010), pp.13-21.
37 Federal Highway Administration, Urban Tree and Landscape Safety, Task T-06-005(McLean, VA: February 2, 2009), p. 85.
38 Ruth Hunter, et al., "The impact of interventions to promote physical activity in urban green space: A systematic review and recommendations for future research," Social Science and Medicine, Volume 124, (January 2015): 246-256.
39 Hannah Cohen-Cline, Eric Turkheimer, and Glen Duncan, "Access to green space, physical activity and mental health: a twin study," Journal of Epidemiology & Community Health, Volume 69, Issue 6, (June 2015): 523-529.
40 D.J. Nowak and G.M. Heisler, Air Quality Effects of urban Trees and Parks, (Ashburn, VA: National Recreation and Park Association, 2010), p.3.
41 FHWA, Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers, FHWA-HEP-16-020 (Washington, DC: December 2015). Available at: https://www.environment.fhwa.dot.gov/ecosystems/vegmgmt_pollinators.asp.
42 American Association of State Highway and Transportation Officials, Roadside Design Guide, 4th Edition, Washington DC: AASHTO, 2011, p.10-15.