Guidelines for Cost-Effective Safety Treatments of Roadside Ditches (2021) / Chapter Skim
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D-2 The roadside ditch design guidelines are presented in Figure D.1 through Figure D.6. Following is a list of variables used in the guidelines.
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D-3 foreslope and backslope combination of interest on the appropriate chart. If the point falls on or inside the curve representing the adjusted encroachment rate, the foreslope and backslope combination is acceptable.
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D-4 Figure D.1. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and horizontal curvature of less than 3 degrees.
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D-5 Figure D.2. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and horizontal curvature of less than 3 degrees.
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D-6 Figure D.3. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and horizontal curvature of greater than or equal to 3 degrees and less than 6 degrees.
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D-7 Figure D.4. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and horizontal curvature greater than or equal to 3 degrees and less than 6 degrees.
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D-8 Figure D.5. Roadside ditch design guidelines for ditch bottom width of less than 6 ft and horizontal curvature of greater than or equal to 6 degrees.
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D-9 Figure D.6. Roadside ditch design guidelines for ditch bottom width of greater than or equal to 6 ft and horizontal curvature of greater than or equal to 6 degrees.
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D-10 Figure D.7. Encroachment rate based on AADT for divided and undivided highway types.
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D-11 Table D.2. Adjust Factors for ER Based on Vertical Grade Grade*
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D-12 Roadway Details Roadway type: rural two-lane undivided. Bidirectional AADT: 3,000 vpd.
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D-13 EXAMPLE B Figure D.9. Example B -- Proposed roadside ditch geometry.
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D-14 6. Plot a point on Figure D.4 corresponding to the slopes of the proposed channel in Figure D.9.
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