Design Guidelines for Mitigating Collisions with Trees and Utility Poles (2022) / Chapter Skim
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From page 24... ...
24 This chapter presents computational examples to illustrate the benefit-cost analysis method using the results of the recommended crash prediction model. The following five examples are presented: • Benefit-Cost Example 1 -- Removal of an Isolated Roadside Tree • Benefit-Cost Example 2 -- Removal of a Continuous Group of Roadside Trees • Benefit-Cost Example 3 -- Relocation of an Isolated Utility Pole • Benefit-Cost Example 4 -- Relocation of an Extended Series of Utility Poles • Benefit-Cost Example 5 -- Removal of an Extended Series of Utility Poles and Replacement with Underground Utilities The examples presented here are intended to illustrate how proposed improvements can be assessed with the crash prediction model and the benefit-cost method.
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From page 25... ...
Benefit-Cost Analysis Examples 25 Variable Name Before Condition After Condition NROR 0.0013 0.0000 NROR-left 0.0000 0.0000 NROR-right 0.0013 0.0000 NROR-K 0.0001 0.0000 NROR-A 0.0002 0.0000 NROR-B 0.0005 0.0000 NROR-C 0.0005 0.0000 NROR-PK 0.0001 0.0000 NROR-PI-A 0.0003 0.0000 NROR-PI-B 0.0006 0.0000 NROR-PI-C 0.0008 0.0000 LikelihoodROR 1.0000 1.0000 SeverityROR-left 0.0000 0.0000 SeverityROR-right 17.8450 0.0000 RSSROR-left 0.0000 0.0000 RSSROR-right 2.8674 0.0000 Table 10. Computational results with crash prediction model before and after removal of an isolated tree 6 ft from the traveled way of a rural 2-lane highway with an AADT of 1,000 vpd.
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From page 26... ...
26 Design Guidelines for Mitigating Collisions with Trees and Utility Poles For the initial case, the B/C for removing the single tree can be computed with Equation (17) as follows: [ ]
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From page 27... ...
Benefit-Cost Analysis Examples 27 The following percentage changes in the values shown in Table 11 represent the effects of key differences in roadway design, traffic control, and traffic speed factors on average crash reduction and benefit-cost ratio: Horizontal Curvature (Base Condition: Tangent) • Moderate curvature 81% increase • Sharp curvature 251% increase • Very sharp curvature 502% increase Lane Width (Base Condition: 12 ft)
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From page 28... ...
28 Design Guidelines for Mitigating Collisions with Trees and Utility Poles Variable Name Before Condition After Condition NROR 0.0336 0.0000 NROR-left 0.0000 0.0000 NROR-right 0.0336 0.0000 NROR-K 0.0026 0.0000 NROR-A 0.0060 0.0000 NROR-B 0.0126 0.0000 NROR-C 0.0124 0.0000 NROR-PK 0.0028 0.0000 NROR-PI-A 0.0064 0.0000 NROR-PI-B 0.0156 0.0000 NROR-PI-C 0.0200 0.0000 LikelihoodROR 1.0000 1.0000 SeverityROR-left 0.0000 0.0000 SeverityROR-right 17.8450 0.0000 RSSROR-left 0.0000 0.0000 RSSROR-right 2.8674 0.0000 Table 13. Computational results with crash prediction model before and after removal of a tree group 6 ft from the traveled way of a rural 2-lane highway with an AADT of 1,000 vpd.
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From page 29... ...
Benefit-Cost Analysis Examples 29 Table 14 shows the computed crash reductions and benefit-cost ratios for each value of AADT and distance from the traveled way to the roadside trees considered. The results show that, under the specified conditions, removal of trees generally becomes cost-effective between AADTs of 1,000 and 5,000 vpd for tree groups within 30 to 35 ft of the traveled way.
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From page 30... ...
30 Design Guidelines for Mitigating Collisions with Trees and Utility Poles For the initial case analyzed for Benefit-Cost Example 3, with a roadway AADT of 1,000 vpd and the individual utility pole in the before condition located 6 ft from the edge of the traveled way, the predicted annual crashes estimated with the crash prediction model are as shown in Table 16. The table shows both the crash predictions obtained from the model and intermediate results as derived from Equations (1)
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From page 31... ...
Benefit-Cost Analysis Examples 31 Table 11 for Benefit-Cost Example 1, shows that utility pole relocation projects are generally not as cost-effective as tree removal projects because of the higher cost of relocating a utility pole. The table shows that utility relocation projects typically become cost-effective on rural 2-lane undivided highways with AADTs between 1,000 and 5,000 vpd for utility poles located within 15 to 25 ft of the traveled way.
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From page 32... ...
32 Design Guidelines for Mitigating Collisions with Trees and Utility Poles values of 1,000, 5,000, and 10,000 vpd and the distance of the tree to be removed from the outside edge of the traveled way was 6 ft and from 10 to 40 ft in increments of 5 ft. There should be economies of scale in relocating multiple utility poles in the same vicinity.
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From page 33... ...
Benefit-Cost Analysis Examples 33 of utility poles can be cost-effective, even for roads with AADTs as low as 1,000 vpd, when the utility poles are near the traveled way. Because of economies of scale in the cost of utility pole relocation, projects involving relocation of multiple utility poles appear to be more cost-effective than projects involving relocation of a single utility pole, as can be seen from comparing the results in Tables 17 and 20.
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From page 34... ...
34 Design Guidelines for Mitigating Collisions with Trees and Utility Poles Table 22 shows the computed crash reductions and benefit-cost ratios for each value of AADT and distance from the traveled way to roadside utility poles considered. The results shown in Table 22 confirm the indications in the literature (see Section 5.7)
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