RECONNAISSANCE SURVEY
METHODS FOR HIGHWAY ROUTE SELECTION
METHODS FOR HIGHWAY ROUTE SELECTION
Reconnaissance survey is done to examine the general
character of the area for the purpose of determining the most feasible route or
routes for further more detailed investigations.
character of the area for the purpose of determining the most feasible route or
routes for further more detailed investigations.
Data collected from reconnaissance
survey is used for feasibility study of all different routes, preparation of
approximate estimates of quantities and costs. This helps in selection of most
suitable alternatives. This survey also helps in determining any deviations
required in the basic geometric standards to be adopted for the highway facility.
survey is used for feasibility study of all different routes, preparation of
approximate estimates of quantities and costs. This helps in selection of most
suitable alternatives. This survey also helps in determining any deviations
required in the basic geometric standards to be adopted for the highway facility.
Reconnaissance survey is generally not
required for the work consisting of improvements to existing roads unless
bypass roads are involved.
required for the work consisting of improvements to existing roads unless
bypass roads are involved.
Reconnaissance Survey Methods:
The reconnaissance survey methods may be conducted in the
following sequence:
following sequence:
a) Study of topographical survey sheets, agricultural, soil,
geological and meteorological maps and aerial photography.
geological and meteorological maps and aerial photography.
b) Aerial photography wherever necessary and feasible, and
c) Ground reconnaissance including another round of serial
reconnaissance for inaccessible and difficult stretches, where required.
reconnaissance for inaccessible and difficult stretches, where required.
Study of Survey Sheets and Maps:
Reconnaissance survey starts with a
study of the all available maps. After study of the topographical features on
the maps, a number of economical alignments feasible in a general way are
selected keeping in view the following points:
study of the all available maps. After study of the topographical features on
the maps, a number of economical alignments feasible in a general way are
selected keeping in view the following points:
(i) The alignment to take into account
all the control points and to be shortened and more economical compatible with
requirements of gradients and curvature.
all the control points and to be shortened and more economical compatible with
requirements of gradients and curvature.
(ii) Shape of the alignment.
(iii) Avoidance as far as possible of
marshy ground, steep terrains, unstable hill features and areas subject to
severe climatic conditions, flooding and inundation.
marshy ground, steep terrains, unstable hill features and areas subject to
severe climatic conditions, flooding and inundation.
(iv) Need of connecting important
villages and towns.
villages and towns.
(v) Bridging problems, and
(vi) Need to preserve environment and
maintain ecological balance.
maintain ecological balance.
The aerial photographs, if taken may
be to a scale of 1:20000 to 1:50000 to supplement the information from
topographic maps. If stereoscopic techniques are applied, aerial photographs
can yield quantitative data, and if studied by a skilled photo interpreter,
significant soil and subsoil information.
be to a scale of 1:20000 to 1:50000 to supplement the information from
topographic maps. If stereoscopic techniques are applied, aerial photographs
can yield quantitative data, and if studied by a skilled photo interpreter,
significant soil and subsoil information.
Aerial Reconnaissance Survey:
An
aerial reconnaissance will provide a bird’s eye view of the alignments under
consideration along with the surrounding area. It will help to identify factors
which call for rejection or modification of any of the alignments. Final
decision about the alignments to be studied in detail on the ground could be
taken on the basis of the aerial reconnaissance.
aerial reconnaissance will provide a bird’s eye view of the alignments under
consideration along with the surrounding area. It will help to identify factors
which call for rejection or modification of any of the alignments. Final
decision about the alignments to be studied in detail on the ground could be
taken on the basis of the aerial reconnaissance.
Ground Reconnaissance Survey:
Ground reconnaissance consists of
general examination of ground by walking or riding along the probable routes
and collecting all available information necessary for evaluating the same. In
the case of hill sections, it may be advantageous sometime to start the
reconnaissance from an obligatory point situated close to the top. If an area
is inaccessible for the purpose of ground reconnaissance, aerial method should
be used to clear the doubts.
general examination of ground by walking or riding along the probable routes
and collecting all available information necessary for evaluating the same. In
the case of hill sections, it may be advantageous sometime to start the
reconnaissance from an obligatory point situated close to the top. If an area
is inaccessible for the purpose of ground reconnaissance, aerial method should
be used to clear the doubts.
While reconnoitering on the ground, it
is advisable to leave reference pegs to facilitate further survey operations.
is advisable to leave reference pegs to facilitate further survey operations.
Instruments generally used for ground
reconnaissance include compass, Abney level / alti-meter, pedometer, aneroid
barometer, clinometers, ghat tracer etc. Walkie-talkie sets are useful for communication,
particularly in difficult terrain.
reconnaissance include compass, Abney level / alti-meter, pedometer, aneroid
barometer, clinometers, ghat tracer etc. Walkie-talkie sets are useful for communication,
particularly in difficult terrain.
Use of instruments mentioned above to
obtain ground slopes, maximum gradients, elevation of critical summits or
stream crossings and location of obligatory points, serves as a check on the
maps being used.
obtain ground slopes, maximum gradients, elevation of critical summits or
stream crossings and location of obligatory points, serves as a check on the
maps being used.
Reconnaissance Survey Reports:
Based on information collected during
the reconnaissance survey, a report should be prepared. The report should
include all relevant information collected during the survey and a plan to the
scale of 1:50000 showing the alternative alignments studied along with their
general profile and rough cost estimate. It should also discuss the merits and
demerits of the different alternatives to help the selection of one or more
alignments for detailed survey and investigation.
the reconnaissance survey, a report should be prepared. The report should
include all relevant information collected during the survey and a plan to the
scale of 1:50000 showing the alternative alignments studied along with their
general profile and rough cost estimate. It should also discuss the merits and
demerits of the different alternatives to help the selection of one or more
alignments for detailed survey and investigation.
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