Design Guidelines for Horizontal Sightline Offsets (2019) / Chapter Skim
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59 A P P E N D I X A Computation of HSOs This appendix addresses the computation of horizontal sightline offsets. A.1 Presentation of HSOs in the AASHTO Green Book The Green Book (AASHTO 2011)
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60 Design Guidelines for Horizontal Sightline Offsets Figure A-1. Diagram illustrating components for determining horizontal sight distance (AASHTO 2011)
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Computation of HSOs 61 • The offset to the horizontal sight obstruction that is needed to provide the design stopping sight distance divided by the maximum offset determined with Equation (A-2)
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62 Design Guidelines for Horizontal Sightline Offsets Glennon (1987) used a graphical method to develop offset ratios similar to those developed by Raymond.
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Computation of HSOs 63 A.5 Computational Method for HSOs Developed by Mauga Two related papers by Mauga (2014, 2015b) present an alternative computational method for determining HSO for horizontal curves.
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64 Design Guidelines for Horizontal Sightline Offsets C1…C6 = constant values (defined by equations in text) Figure A-5.
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Computation of HSOs 65 A.5.1 Case 1(a) – Long Curve (L > S)
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66 Design Guidelines for Horizontal Sightline Offsets (A-16)
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Computation of HSOs 67 A.5.4 Case 2(a) – Short Curve (L < S)
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68 Design Guidelines for Horizontal Sightline Offsets (A-41)
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Computation of HSOs 69 A.6 Comparison of Methods Figure A-7 shows a comparison by Mauga (2014) of his analytical model with the graphical procedure and the approaches used by Raymond (1972)
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70 Design Guidelines for Horizontal Sightline Offsets A.7 Computation of Roadside Clear Areas Since sight distance is measured from the centerline of the inside lane and the travel lanes and shoulder are, by definition, clear of sight obstructions (with the possible exception of stopped vehicles on the shoulder) , the value of horizontal sightline offset, m, is only of practical importance to design where: (A-58)
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