The various factors which affect the selection and deviation of highway alignment are
A) Obligatory points: Obligatory points are the controlling points that govern the highway alignments. The obligatory points are responsible for the deviation of highway. There are two types of obligatory points.
i)Positive obligatory points: Points through which an alignment is allowed to pass – for eg. bridge site, important city, etc.
ii) Negative obligatory points: Points through which an alignment should not pass. – for eg. religious places like temples and churches, any water body, monuments, valleys, etc.
B) Traffic: The alignment of road should be made in such a way that it should meet the traffic requirements. To know the trend of traffic, origin and destination study should be carried out. Also, the traffic flow patterns and traffic forecasting for the future should be studied before making the alignment of road.
C) Geometric design: There are various factors which determines the geometric design of highway, these factors are gradient, radius of curve and sight distance. The alignment should not disturb the speed of vehicle. If such condition arises, the alignment is required to be changed through the new path.
D) Economy: The economy is one of the most important factors to keep in mind while deciding the alignment of the road. The costs like construction cost, maintenance cost, and operation cost are minimized up to a possible extent, without compromising the quality of work.
E) Other consideration: Various other factors which govern the alignment are drainage consideration, hydrological factors, political consideration, etc. The vertical alignment is directly dependent on drainage condition. The foreign territory coming across a straight alignment will necessitate deviation of alignment around the foreign land. At times the alignment is decided only on strategic (रणनीतिक) consideration.
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