Guidelines for Cost-Effective Safety Treatments of Roadside Ditches (2021) / Chapter Skim
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215 CHAPTER 10. GUIDELINE DEVELOPMENT INTRODUCTION New findings emanating from this research are presented in entirety in the graphs shown in Figures 8.29 through 8.31 of Chapter 8.
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216 Figure 10.1. Preferred design envelope graph for HC of less than 3 degrees, ditch bottom width of 0 to 4 ft, and ER of 0.75.
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217 Figure 10.2. Simplified design envelope graph containing a single curve that represents all the foreslope widths.
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218 PROPOSED DESIGN GUIDELINES FOR ROADSIDE DITCH DESIGN The roadside ditch design guidelines are presented in Figure 10.4 through Figure 10.9. Following is a list of variables used in the guidelines: HC -- Horizontal curvature (degrees)
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219 If the roadway has both HC and vertical grade, adjustment factors are determined for both and each is multiplied by the previously determined baseline ER rate for use in the ditch design guidelines. After obtaining the appropriate ER, the designer determines which of the six figures (from Figure 10.4 through Figure 10.9)
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220 Figure 10.4. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and HC of less than 3 degrees.
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221 Figure 10.5. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and HC of less than 3 degrees.
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222 Figure 10.6. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and HC of greater than or equal to 3 degrees and less than 6 degrees.
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223 Figure 10.7. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and HC greater than or equal to 3 degrees and less than 6 degrees.
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224 Figure 10.8. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and HC of greater than or equal to 6 degrees.
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225 Figure 10.9. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and HC of greater than or equal to 6 degrees.
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226 Figure 10.10. ER based on AADT for divided and undivided highway types.
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227 Table 10.2. Adjust Factors for ER Based on Vertical Grade Grade*
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