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Appendix-F - Geometric Design Manual-2002 Appendix F...

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Appendix F Geometric Design Manual-2002 Procedure for Design Ethiopian Roads Authority Page F-1 F. P ROCEDURE FOR D ESIGN F.1 Introduction This chapter has been prepared as a guide and checklist for personnel engaged in road design. It is not intended as a textbook nor should the contents be considered mandatory in the design of all road projects. It is recognized that whilst the design procedure is generally the same for any project, there are many specific issues, which the designer must consider in proceeding with the design of each individual project Reference is made in this chapter to the procedures to be followed in the preparation of data for processing by computer-aided methods. However, whether the designer uses manual or computer methods, he must always be aware that good engineering judgment must be exercised at all times. A complete review of all field data, project requirements, economics and applicable specifications must be considered in order to produce the most technically sound and economic design for each project. The designer must also be aware of any relevant safety and environmental regulations and incorporate these features in the design. The chapter ends with the presentation of a checklist for road link design. F.2 Review of Field Data Horizontal Alignment-In many instances the designer has little control over the location of the horizontal alignment due to right-of-way restrictions, previous commitments with local community groups, or other factors. The following items should be considered: 1. Review topographical data along with horizontal alignment to insure that steep gradients are avoided where possible. 2. Review topography to insure that alignment does not parallel major drainages, which may result in channel changes, extra culvert lengths due to skews, etc. 3. Review curve data to insure that degree of curvature meets the allowable maximum for the required design speed. Also avoid broken curves in alignment or short tangents on switch back curves that make it impossible to design adequate super elevation transitions. Projects to be designed by computer-aided methods should have horizontal alignment data submitted as follows: 1. If the project has been located on photogrammetric manuscripts, the designer need only submit beginning station and degree of curvature and coordinates of every horizontal P.I. 2. If the project has been located by ground surveys, the designer should submit horizontal alignment data in notebook form.
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Appendix F Procedure for Design Geometric Design Manual-2002 Page F-2 Ethiopian Roads Authority The designer will furnish ERA with copies of horizontal alignment listing (HAL), which will list all stations and coordinates of P.C., P.I. and P.T. of each curve, including curve data.
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