FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

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9.4.A. Geometric Design. (continued)At the beginning of a design, the depth of the pavement structure may be arrived at by an assumptionbased on experience or by comparing with the depths used on an adjacent project. Following ageotechnical investigation, the designer will adjust the assumed depth accordingly. The geotechnicalinvestigation usually takes place after a line and grade have been established.For RRR projects, the riding quality of an asphalt surface may be improved by providing a leveling course.This additional depth may increase the pavement structure capabilities and merits consideration in the finalpavement design when leveling is relatively uniform over the length of the project. If a field review of theproject is not practical, the designer should increase asphalt concrete pavement quantities by 20 percent foruse as leveling material. See Chapter 6 for additional details on the design of asphalt and concretepavements.b. Profile Grade Location and Cross Slope. The standard location of profile grade on the highway crosssection is at centerline or low side of the superelevated section for all two-lane highways.The cross slope on tangents on paved highways shall be from 1.5 to 2.0 percent.Normally, the cross slopes on gravel surfaced roads shall be 3 to 4 percent.The shoulder cross slope should be the same as the adjacent traffic lane. With curb sections or when theshoulder surface is an asphalt surface treatment, aggregate, or turf, increasing the slope helps to facilitatedrainage. In these cases, consider cross slopes of 4 to 6 percent. On super elevated curves, the roll-over incross slope on the outside of the curve should not exceed 8 percent.The cross slope on the tops of base courses and the subgrade is usually the same as on the finishedpavement. In some cases it is desirable to have a reverse slope on the subgrade (on the high side of curvesand outside the edge of the pavement) to prevent moisture from entering the base.c. Lane and Shoulder Widths. The Green Book and other agency standards show lane and shoulderwidths for each functional classification for various design speeds and traffic volume ranges.When the percentage of trucks or recreational vehicles is high in comparison to the ADT, considerincreasing lane widths.d. Foreslopes. Foreslopes ensure the stability of the roadway and provide a reasonable opportunity forrecovery of an out-of-control vehicle. The foreslope, the slope from the edge of the surfaced shoulder tothe edge of the subgrade shoulder, should not be steeper than the slope ratios shown in Table 9-7, unlessguardrail is placed (Detail designs should be in accordance with the Roadside Design Guide, AASHTO,1996).The slope from the edge of the subgrade shoulder to the bottom of the ditch should normally be anextension of the foreslope.9 - 40
9.4.A. Geometric Design. (continued)Table 9-7Foreslope RatiosGuidelines for Foreslopes Including Ditch SectionsDesign VolumeDesign Speed (km/h)(ADT) 30 40 50 60 70 80 90 100 110Less than 250 1:3* 1:3* 1:3* 1:3* 1:3* 1:3* 1:4 1:4 1:5250 to 500 1:3* 1:3* 1:3* 1:3* 1:4 1:4 1:4 1:4 1:5501 to 1000 1:3* 1:3* 1:3* 1:3* 1:4 1:4 1:5 1:5 1:51001 to 3000 1:3* 1:3* 1:3* 1:4 1:4 1:4 1:5 1:5 1:6Greater than 3000 1:4 1:4 1:4 1:4 1:5 1:5 1:6 1:6 1:6*Slopes steeper than 1:4 are traversable but are not considered recoverable and should be avoided.On RRR projects, the proposed work on the roadway may affect the foreslopes from the edge of pavementto the hinge point of the fill slope and ditch foreslopes.The following points should also be noted:When the existing roadway geometrics are retained and the foreslopes are steeper than 1:4, reshapingto provide a flatter foreslope is desirable.There are cases where the roadbed width will not accommodate foreslopes of 1:3 or flatter. There alsomay be restrictions on filling of ditches to provide width or widening of embankments. When thisoccurs, consider strengthening the existing pavement structure through a recycling-in-place processrather than overlaying the project. A narrower pavement width to maintain a 1:3 foreslope and preventan undesirable edge drop-off is also a reasonable solution.It is desirable to flatten crossroad/road approach foreslopes to 1:10. Provide at least a 1:4 minimumslope. Move the crossroad/road approach drainage away from the mainline to maintain the integrity ofthe clear zone and reduce the length of pipe required.e. Roadway Ditches. The ditch cross section must be adequate to accommodate drainage of thepavement and cutslope. Chapter 7 covers the details of hydraulic design.Ditches should have a streamlined cross section for safety (Chapter 8) and ease of maintenance. Wideditch bottoms are used in rock fallout areas as well as in projects designed with side borrow.Generally, roadway ditches have a "v" shape formed by the foreslope from the subgrade shoulder and cutslope. The depth of the ditch is dependent on hydraulic needs. It should normally be from 150 to 300millimeters below subgrade for safety and maintenance purposes. When hydraulic needs dictate ditches ofgreater capacity, a flat bottom ditch takes precedence over deepening the v-ditch.The designer should obtain computer plots of the roadway ditch profiles to check for sags in the ditch line.These profiles will show where the installation of culverts or the construction of special ditch grades willeliminate ponding.9 - 41
Page 2 and 3: TABLE OF CONTENTS9.4 PS&E DEVELOPME
Page 4 and 5: TABLE OF CONTENTS9.4 PS&E DEVELOPME
Page 6 and 7: LIST OF TABLESTablesPage9-1 Design
Page 8 and 9: 9.1.B. Design Standards.B. Design S
Page 10 and 11: 9.1.B. Design Standards. (continued
Page 12 and 13: 9.1.B. Design Standards. (continued
Page 14 and 15: 9.2 GUIDANCE AND REFERENCESThe publ
Page 16 and 17: 9.3 INFORMATION GATHERINGThe design
Page 18 and 19: 9.3.C. Accident Data.C. Accident Da
Page 20 and 21: 9.4.A. Geometric Design. (continued
Page 24: 9.4.A. Geometric Design. (continued
Page 65 and 66: 9.4.B. Intersection Design. (contin
Page 77 and 78: 9.4.C. Earthwork Design.C. Earthwor
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Page 85 and 86: 9.4.D. Earth Retaining Structures.
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9.4.E. Drainage Design.E. Drainage
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9.4.E. Drainage Design. (continued)
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9.4.F. Other Design Elements.F. Oth
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9.4.F. Other Design Elements. (cont
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9.4.G. Right-of-Way and Utilities.G
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9.4.G. Right-of-Way and Utilities.
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9.4.H. Reviews.H. Reviews. PS&E dev
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9.4.I. Plans.I. Plans. Plans consis
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9.4.J. Engineer's Estimate.J. Engin
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9.4.J. Engineer’s Estimate. (cont
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9.4.K. Specifications.K. Specificat
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9.4.K. Specifications. (continued)W
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9.4.K. Specifications. (continued)I
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9.4.L. Contract Assembly.L. Contrac
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9.6 STANDARD FORMATA. Plans. Projec
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9.6. Standard Format. (continued)Ta
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9.6. Standard Format. (continued)A
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9.6. Standard Format. (continued)Ex
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9.6. Standard Format. (continued)Sh
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9.6. Standard Format. (continued)(1
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Project Number:Project Name:Descrip
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EXHIBIT 9.38APPROVED STANDARD DRAWI
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EXHIBIT 9.38APPROVED STANDARD DRAWI
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FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

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