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The next important factor that affects the geometric design is the topography.
It is easier to construct roads with required standards for a plain terrain.
However, for a given design speed, the construction cost increases multiform
with the gradient and the terrain.
Therefore, geometric design standards are different for different terrain to
keep the cost of construction and time of construction under control.
This is characterized by sharper curves and steeper gradients.
In addition to design speed and topography, there are various other factors
that affect the geometric design and they are briefly discussed below:
- Vehicle: :The dimensions, weight of the axle and operating
characteristics of a vehicle influence the design aspects such as width of the
pavement, radii of the curve, clearances, parking geometrics etc.
A design vehicle which has standard weight, dimensions and operating
characteristics are used to establish highway design controls to accommodate
vehicles of a designated type.
- Human: The important human factors that influence geometric
design are the physical, mental and psychological characteristics of the driver
and pedestrians like the reaction time.
- Traffic: It will be uneconomical to design the road for peak
traffic flow.
Therefore a reasonable value of traffic volume is selected as the design hourly
volume which is determined from the various traffic data collected.
The geometric design is thus based on this design volume, capacity etc.
- Environmental: Factors like air pollution, noise pollution etc.
should be given due consideration in the geometric design of roads.
- Economy: The design adopted should be economical as far as
possible.
It should match with the funds alloted for capital cost and maintenance cost.
- Others: Geometric design should be such that the aesthetics of the
region is not affected.
We will discuss on alignment, classification and factors affecting GD.
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