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126 Recommended Text for Potential Use in a Future Edition of the AASHTO Roadside Design Guide This appendix presents text recommended for use in a future edition of the AASHTO RDG (AASHTO 2011) to incorporate the results of this research. Potential inserts concerning both utility poles and trees are presented. The recommended RDG text does not attempt to present the full details of the crash prediction method developed in the research, but rather makes reference to the design guidelines document that presents all of the information that a designer would need to apply the method. Insert at the end of RDG Section 4.8 (Utility Poles) Roadside improvement programs for relocating utility poles should identify opportunities to reduce utility-pole-related crashes and prioritize potential projects. The highest priorities for improvement projects should be utility poles that are located close to the roadway traveled way on higher volume and higher speed roads and are not shielded by guardrail or other traffic barriers. A crash prediction method that can provide quantitative estimates of annual crashes likely to occur involving an individual utility pole or an extended series of utility poles is presented as part of the design guidelines in NCHRP Report 1016 (11). This method can provide quantitative estimates of annual crashes likely to occur involving an individual utility pole or for a series of poles and is available for application by highway agencies in planning utility pole relocation projects. The crash prediction method includes a model to estimate the frequency of utility-pole-related crashes for individual poles or a series of poles. The estimated crash counts can be broken down by crash severity level and can be used to estimate the number of persons likely to be injured in those crashes. These estimated crash frequencies and severities provide a basis for estimating the annual and long-term benefits of potential utility pole relocation projects and for conducting economic analyses to determine the benefit-cost ratio and net benefits of specific proposed projects. Projects can be prioritized based on their estimated crash reduction and their benefit-cost ratio. The design guidelines in NCHRP Report 1016 (11) present examples of benefit-cost analyses for typical utility pole relocation projects on rural two-lane highways. These examples represent only one potential scenario or base caseâa project on a roadway with characteristics that minimize roadside encroachments--but they show that utility pole relocation projects can be cost- effective. For roadways of this type, relocating a single utility pole is not typically cost-effective for a rural two-lane undivided highway with an AADT of 1,000 veh/day, but does typically become cost-effective for AADTs of 5,000 veh/day if the utility pole is within 15 ft of the traveled way. For a rural two-lane undivided highway with an AADT of 10,000 veh/day, relocation of a single utility pole may be cost-effective for utility poles within 25 ft of the traveled way. Because of economies of scale in improvement costs, relocating a series of utility poles may be more cost-effective than relocating a single utility pole The benefit-cost examples in the design guidelines (11) show how the crash prediction and benefit-cost analysis methods can be applied to assess specific potential improvement projects; these methods can also be applied to projects on rural two-lane undivided highways with roadway designs that would have
127 more roadside encroachments than the base case and to rural four-lane undivided highways and rural four-lane divided nonfreeways. Benefit-cost analysis shows that removing overhead utility lines and placing the utility lines underground is often not cost-effective, regardless of the roadway AADT and the location of the utility poles with respect to the roadway traveled way. Provision of underground utility lines is typically done for aesthetic reasons rather than because the crash reduction benefits exceed the project cost. While the benefit-cost examples described above, and presented in the design guidelines (11) use typical or representative input data, these inputs vary substantially from site to site, so the most reliable results will be obtained from analyses that use site-specific roadway characteristics, utility pole location, and improvement cost data. A spreadsheet tool is available with the design guidelines for performing such analyses efficiently. Insert at the end of RDG Section 4.9 (Trees) Roadside improvement programs for removing trees should identify opportunities to reduce tree- related crashes and prioritize potential projects. The highest priorities for improvement projects should focus on trees that are located close to the roadway traveled way on higher volume and higher speed roads and are not shielded by guardrail or other traffic barriers. A crash prediction method that can provide quantitative estimates of annual crashes likely to occur involving an individual tree or a group of trees is presented as part of the design guidelines in NCHRP Report 1016 (11). This method can provide quantitative estimates of annual crashes likely to occur involving an individual tree or a series of trees and is available for application by highway agencies in planning tree removal projects. The crash prediction method includes a model to estimate the frequency of tree-related crashes for individual trees or for tree groups. The estimated crash counts can be broken down by crash severity level and can be used to estimate the number of persons likely to be injured in those crashes. These estimated crash frequencies and severities provide a basis for estimating the annual and long-term benefits of potential tree removal projects and for conducting economic analyses to determine the benefit-cost ratio and net benefits of specific proposed projects. Projects can be prioritized based on their estimated crash reduction and their benefit-cost ratio. The design guidelines in NCHRP Report 1016 (11) present examples of benefit-cost analyses for typical tree removal projects on rural two-lane highways. These examples represent only one potential scenario or base caseâa project on a roadway with characteristics that minimize roadside encroachments--but they show that tree removal projects can be cost-effective. For roadways of this type, removing a single tree may be cost-effective on a rural two-lane undivided highway even with an AADT as low as 1,000 veh/day, and is very cost-effective at higher AADTs. For projects involving removal of continuous tree groups, there may be economies of scale in improvement costs per tree removed, but there may be many closely spaced trees to be removed if the trees are spaced close to one another along the roadside. As a result, removal of continuous tree groups may, in some cases, be less cost-effective than removing a single tree. The benefit-cost examples in the design guidelines (11) show how the crash prediction and benefit-cost analysis methods can be applied to assess specific potential projects; these methods can also be applied to projects on rural two-lane undivided highways with roadway designs that
128 would have more roadside encroachments than the base case and to rural four-lane undivided highways and rural four-lane divided nonfreeways. While the benefit-cost examples described above, and presented in the design guidelines (11), use typical or representative input data, these inputs vary substantially from site to site, so the most reliable results will be obtained from analyses that use site-specific roadway characteristics, tree location, and improvement cost data. A spreadsheet tool is available with the design guidelines for performing such analyses efficiently. While tree-related crashes are a key roadside design issue, transportation agencies must recognize in developing strategies for reducing the potential for tree-related crashes that trees are a desirable feature of the landscape and have an important aesthetic value to communities and, indeed, to motorists. The presence of trees makes a community attractive to residents and visitors. Motorists enjoy driving through natural landscapes, and trees are an important element of such landscapes. Trees also make urban communities appear attractive and well planned. At the same time, the potential for motorist deaths and injuries in collisions with trees is a substantial traffic safety issue that deserves to be addressed. Transportation agencies should consult with communities and motorist organizations in developing policies to reduce tree- related crashes. Alternatives to tree removal, such as provision of traffic barriers between the roadway and trees, should be considered, where appropriate. Reference to be added to RDG Chapter 4: 11. Potts, I.B., and D.W. Harwood, NCHRP Report 1016: Design Guidelines for Mitigating Collisions with Trees and Utility Poles, National Cooperative Highway Research Program, Transportation Research Board, 2022. [NOTE: This reference cites the separate design guidelines document prepared in NCHRP Project 17-82, not this final report.]
