The document discusses the process of highway alignment planning and design. It describes the key factors that must be considered, including obligatory points, traffic needs, geometric design standards, economics, and other special requirements for different terrain. The alignment selection process involves four main survey stages - map study, reconnaissance, preliminary survey, and final detailed survey. The goal is to find an alignment that meets all important requirements in the most economical way possible.

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Highway Alignment
Portion of centerline of the highway on ground

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Alignment
o Horizontal: Straight path, horizontal deviations,
curves
o Vertical: Changes in the gradient, vertical curves
Construction cost, maintenance cost, operational cost,
accident rate
Once fixed, it is difficult and costly to change in future
Enough care is necessary as error may lead to losses
in Initial, Maintenance or Operation costs

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Basic Requirements
o Short: Straight is shortest and hence cheapest, may
not be possible always
o Easy: w.r.t. Construction, Maintenance, Vehicle
Operation
o Safe: w.r.t. Construction. Maintenance, Operation,
Slopes, land slides
o Economical: Total cost of construction as well as
maintenance and vehicle operation should be
minimum
o Should have max. utility w.r.t service to Public

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Factors Affecting Alignment
All the requirements are rarely fulfilled by any single
alignment. Depends on...
o Obligatory Points
o Traffic
o Geometric Design
o Economics
o Other Considerations

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Obligatory Points
o Controlling points which govern the alignment. Two
types of points . . . .
o Thru which alignment should pass Ex. Bridge site,
intermediate town, quarry
o Thru which should not pass Ex. Religious place, costly
land/structure, pond, valley, problematic area

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Traffic
o Alignment should satisfy the traffic needs
o O-D surveys are undertaken and desire lines are
established
o The proposed alignment should be in tune with the
present as well as future trends and lines

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Geometric Design
Geometric Design factors like
o Slope (Gradient) : Ruling or Design Gradient.
o Radius of curvature: Minimum Radius of Curvature
and Transition Curve.
o Sight distance: Min. SD
govern the alignment
o To accommodate the standards the alignment may
have to be changed

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Economy
o Initial cost depends on the earthwork, so, heavy
cutting and filling avoided
o Besides initial cost the maintenance cost and vehicle
operation cost also to be considered before finalization
Other Consideration
o Slopes are governed by rainfall, seepage flow, GW level,
HFL, and drainage requirements
o Monotony
o Foreign Teritory

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Special Requirements for Hill Roads
Stability:
o Landslides is common problem. Depends on cutting,
filling and side slopes. Care is necessary
Drainage:
o Large number of cross drainages required. For
minimum cost the no. should be min. hence alignment
with minimum c. d. works preferred.

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Special Requirements for Hill Roads
Geometric Standards:
o Relaxed standards for sight dist, curve radius and
other factors. Still affect..
Resisting Length:
o Amount of work for moving one unit of load along the
selected alignment
o Should be as low as possible, i.e. ineffective rise and
excess falls avoided

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Surveys for Location of Alignment
Before finalising the alignment four stages of engineering
surveys are undertaken
o Map study
o Reconnaissance
o Preliminary Survey
o Final location and detailed survey

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Map Study
o Topographic maps, prepared by Survey of India are
studied first
o Many alternatives are marked avoiding ponds, lakes
and valleys
o Approximate location for bridges, hill passes etc. are
considered
o These alternatives are further studied in next step

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Map Study

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Reconnaissance
o Field party visits the marked routes and checks for
obstructions if any, not shown on the map.
o Simple instruments like clinometers, abney level,
barometer are used
o Valleys, Ponds, Structures, hills and obstructions.
o Possibility of geometric std. checked
o Data for no and type of cd works, HFL, GW level, soil
strata, materials for construction, quarry noted down

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Preliminary Survey
Main objectives of the preliminary survey:
o Survey of various alternative alignments
o Compare different proposals
o Estimate quantity of earthwork and other construction
aspects
o To finalise the best alignment

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Preliminary Survey
o Primary traverse
o Topographical features
o Levelling work
o Drainage studies and hydrographical data
o Soil survey: earth work slopes, suitability of materials,
subsoil and surface drainage
o Material Survey
o Traffic Survey: traffic lanes and roadway width,
pavement design
o Determination of final centre line

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Final location and Detailed Survey
o The alignment finalised at the design office after the
preliminary survey is to be first located on the field by
establishing the centre line.
o Final selection marked on ground by pegs using steel
tape and theodolite
o TBM established at 300 m. Precise leveling carried
out. L sect and c/s sect, at closer interval are plotted
o Adequate hydrological and soil data is collected
o Detailed estimates and plans are prepared

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Drawings and Reports
o Key map: proposed and existing roads, and
important places to be connected
o Index map: general topography of the area
o Preliminary survey plans and report
o Detailed plan, L-sect, c/s sect.
o Land acquisition plans
o Masonry works, structures and details
o Material location plans
o Estimates