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Location Surveys


									                      Location Surveys

I.   Traditional Highway Location:
1.   field-oriented work
2.   *Procedures
1)   The first step: Reconnaissance of the area using available
     topographic maps and sometimes an airplane to search
     out feasible routes and determine such primary controls
     as mountain passes or suitable river crossings and to
     locate major obstacles such as steep slopes or marshes
2)   The second step: Reconnaissance of feasible routes for
     rough measures of relative length, difficulty, and cost
3)   The third step: Running in the preliminary or P line, or two
     or more alternate lines on the maps
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                         Location Surveys
4)    The fourth step: laying out the final location or alternate locations
      by study of the maps and profiles after the P line data being
3.    Critical slopes were measured with a hand level; distances and
      angles commonly were measured by transit and taping methods;
      and a profile was taken by differential leveling.
II.   *Modern location practice
1.    Office oriented but parallel to the traditional one
2.    Based on photogrammetric techniques
3.    Field work: aerial survey and ground control; checking out
      incomplete data on the photographs or maps, and soil surveys
      and subsurface exploration.
4.    Procedures of location survey:
(1)   area reconnaissance;
(2)   route reconnaissance;
(3)   preliminary location;
(4)   final location.
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                                  Location Surveys

III. * Preliminary Reconnaissance (area and route)
1.      Purposes: to determine which routes deserve further study, i.e., the
        primary and secondary controls for one or more feasible routes
        within a band of limited width
2.      Primary controls: terminals of the road; vital intermediate points; a
        unique bridge site; single mountain pass
3.      Secondary controls: small settlements for a major highways;
        drainage systems; mountain passes; low points in ridges; swamps
        in low country; cost factors like soil conditions; the numbers and
        sizes of structures; the amount of excavation and embankment
4.      Likewise, for scenic highways, the positions of timbered areas,
        waterfalls, lakes, and other attractions may be primary controls and
        for artery highways, they may be secondary controls or not at all.

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                           Location Surveys
V.   *Preliminary Location
1.   Procedures:
1)   Establishing preferred location within a reasonably narrow band;
2)   Determining a preliminary line;
3)   Reducing the survey data to maps and profiles to a scale of 100 ft
     to 1 in.
2.   Procedures for rural multilane facilities
1.   Separate highways for opposing directions can result in an most
     advantageous location: opposite walls of a canyon or opposite
     sides of streams or small hills; variable median width; different
     alignment and grade line; cheaper than for a constant cross
     section; more pleasant and less monotonous driving; entire
     eliminating of headlight glare

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                                 Location Surveys

VI. *Final Location
1.    The determining of the details of the projected highway by
1)    Shifting the line and adjusting grade;
2)    Setting final horizontal and vertical positioning of structures,
      channels, and other drainage facilities;
3)    Coordinating horizontal and vertical alignments;
4)    Referring sufficient curvature, tangency, and other control points
      on the ground to permit easy location of the line;
5)    Setting bench-marks at relatively close intervals and in positions
      free from disturbance in construction;
6)    Establishing directions of all property lines, distances to
      property corners, and the locations of buildings, fences, and
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                                      Location Surveys

VI. Final Location
7)    Preparing for large-scale topographic maps or other special
      surveys at bridge and structure sites;
8)    Taking into account soil surveys and foundation explorations for
VI.   Homework
1.    What are taken into consideration in a preliminary reconnaissance?
2.    What details are determined in a final location?
3.    True or false statements (refer to pp 18-19 in the synoptic textbook)
4.    Use a table form to illustrate the difference between preliminary
      reconnaissance, preliminary location, and final location.

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