Topo_and_route_selection - Part I Topographic Maps Part I...

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Unformatted text preview: Part I Topographic Maps Part I Topographic Maps and Route Selection Topographic Maps Topographic Maps Primary source of information for the project – Locations of roads and buildings – Elevations and contours – Physical features such as streams and wetlands – Boundaries Contour Lines Contour Lines Represent features of terrain on a 2­D sheet of paper Connect points of equal observation Definitions – Contour interval is the vertical distance between the level surfaces that form the contours – Spot elevations are given for critical points such as peaks, sags, streams, etc. Contour Lines Contour Lines Properties – Must close on themselves – Never branch or cross – Slope between contour lines assumed to be uniform – Contours are perpendicular to maximum slope Contour Lines Contour Lines Properties (cont.) – Separation between contours indicates steepness of slope – Irregular contours signify rough terrain – Smooth lines indicate gradual slopes and changes – Concentric closed contours w/ increasing elevations represent hills Contour Lines Contour Lines Properties (cont.) – Contour lines crossing a stream form V’s that point downstream – Contour lines crossing a ridge crest form U’s that point down the ridge Route Selection Route Selection Determine routes by considering topographic features, human habitation areas, and environmental features considering geometric design controls and criteria The most desirable roadway minimizes environmental impacts, follows the existing topography and compromises between user costs and construction costs Steps to Route Selection Steps to Route Selection 1. 2. 3. 4. 5. Examine natural and manmade features using tools such as topographic maps, aerial photography, geological and soil maps, and ground surveys Identify design and other criteria: R, G, earthwork Identify technically feasible routes trying to minimize cost (on broad level at first) Establish initial horizontal alignments – tangents and horizontal curves Iterative process Route Selection Issues Route Selection Issues Summary Environmental/Cultural/Social Resource Avoidance Design Criteria Earthwork Bridge and Drainage Locations Intersection/Interchange Locations Topographic Features that Require Extensive Work Subsurface/Soil Conditions Part II Horizontal Alignment Part II Horizontal Alignment Design Considerations Minimum Radius Minimum Radius Rmin V = 15(0.01emax + f max ) 2 DESIGN CRITERIA DESIGN CRITERIA Design Speed: A selected speed used to determine Factors that are considered in selection: • Terrain • Anticipated operating speed • Land use • Functional class • the various geometric design features of the roadway. See appropriate GB chapters Design Criteria ­ emax 4 % < emax < 12 % STAs usually adopt emax for entire state or regions – see next bullet (emax = 8 % in PA) Less superelevation “used” in urban environment (therefore “more f”) fmax From AASHTO 2001 GB Side Friction Rural and High-speed Facilities General Design General Design Considerations Alignment should be as directional as possible, but should be consistent with the topography and with preserving properties and community values A flowing line that conforms generally to the natural contours Winding alignment composed of short curves should be avoided General Design General Design Considerations Avoid minimum radius wherever practical Central angle as small as possible Absorb central angle with longest possible curve General Design General Design Considerations “Consistent alignments” – Avoid sharp curvature – Avoid sudden changes from flat to sharp curvature – If needed, a series of successively sharper curves General Design General Design Considerations For smaller deflection angles, avoid short curves that have the appearance of a kink Rules of thumb – Main highways Lcmin = 15*V – High speed freeways Lcmin = 30*V General Design General Design Considerations Provide adequate distance between curves for superelevation runoff and runout (at least 200 feet) Abrupt reversals in alignment should be avoided The “broken back” arrangement of curves should be avoided Horizontal and vertical alignment coordination ...
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This note was uploaded on 06/08/2009 for the course CE 321 taught by Professor Petrucha during the Spring '02 term at Pennsylvania State University, University Park.

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