FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.C. Earthwork Design. (continued)13. Design Steps Using IHDS. The guides listed below represent the more commonly used portions of theIHDS. The designer should refer to IHDS manuals for details in the preparation of input to obtain specificoutput data.Obtain the roadway template, cross-section, and other miscellaneous design information from the approvedstandards for input into the IHDS. See Subsection 9.4.A.7, Geometric Cross Section.(1) Refer to Section 9.4.A in this manual for guidelines on the following topics:- Aesthetic Consideration in Highway Design.- Horizontal and Vertical Alignment Relationship.- Establishing Control Points.- Horizontal Alignment.- Vertical Alignment.Usually more than one horizontal or vertical alignment is studied. These studies deal with cost, alignment,safety, encroachment on waterways, right-of-way, aesthetics, maintenance, and operation. After thecompletion of the studies, one line is selected for further enhancement and refinement of design.(2) Position the design line over the survey data provided using the controls and guidance mentioned above.(3) Compute the station and coordinates of curve and PI points, bearings, tangent lengths, curve lengths, radii,tangent distances, and delta angles using the IHDS horizontal alignment program. Spiral functions arecomputed for spiraled curves.Unless otherwise required, bearings computed to the nearest minute are acceptable. The arc definition forcurves is used with few exceptions.(4) Obtain a plot of the design profile.(5) Using recommended design speed for the route, prepare a progressive listing of each tangent/curve, anddetermine the standard safe speed from charts found in the Green Book. Then adjust this standard safe designspeed for local requirements such as snow and ice conditions, relatively steep grades, and specific requirementsof the cooperating agency.The IHDS program will automatically assign a superelevation rate and runoff length using criteria from theGreen Book, pages 167 to 171. The designer may have to adjust these rates and lengths to comply with thesafe speed guidance.(6) Use the IHDS proposed cross section input file to obtain cross sections. Use input files to obtain end areas,catch points, earthwork volumes, accumulated cut and fill volumes, and the mass ordinates.The IHDS uses the average end area method of determining volumes. The total volume of earthwork is thesum of the volumes of the prismoids formed by adjacent cross sections.9 - 76