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 Surveys4) The fourth step: laying out the final location or alternate locations

by study of the maps and profiles after the P line data being plotted

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.2 Wednesday, April 19, 2023

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 facilities

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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 structures

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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