With the development of
fast moving traffic, the speed, safety and comfort have become the main
requirements of road users now a days. In order to fulfill these requirements,
physical features of a road such as pavement with formation width, right of
way, curves etc. and the speed of road vehicles play a major role while
designing a highway.
Road
Geometrics
The physical features
of a road are known as road geometrics. These include the following elements of
a highway.
Cross-sectional
elements such as right of way, road margins, formation level, camber gradients
etc.
Speed of road vehicle
i.e. design speed, average running speed etc.
Sight distances such as
stopping or non-passing sight distance passing or overtaking sight distance,
intermediate sight distance and lateral sight distance.
Horizontal and vertical
curves.
Super elevation etc.
All these are influenced
by the topography of the land, traffic characteristics and requirements of road
users.
Definitions
Right
of way
The area of land
acquired and reserved for construction and development of a road along its
alignment is known as right-of-way or permanent land and the width of
right-of-way is called permanent land width or road land width.
Road
Margin
The portion of land
width on either side of the roadway of a road are known as road margins. The various
elements included in the road margins are parking lane, frontage road driveway,
cycle track, footpath, guard rail embankment slopes.
Road
Width
The top width of a
highway embankment or bottom width of highway in cutting excluding the side
drains is called roadway width or formation width. Road width comprises of the
width of carriageway including traffic separator, if any, plus the shoulders on
either side.
Carriage
way
The portion of roadway
constructed for movement of vehicular traffic is called carriageway, pavement
or crust.
The width of carriage
way or pavement depends upon the width of traffic, lane and number of lanes
required. According to IRC the carriageway width for single lane traffic is
3.75 m.
Number
of traffic lanes depends on the following factors.
Intensity of traffic
expected in next 10 years.
Type of traffic
expected in next 10 years.
Overall max. width of a
vehicle.
Min. side clearance
required for safe driving.
Shoulders
The portion of the
roadway between the outer edges of the pavement and edges of the top surface of
embankment or inner edges of the side drains in cutting are known as shoulders.
Side
slopes
The slopes given to the
sides of earthwork of a road in embankment or in cutting for its stability are
called side slopes.
Berms
The portion of land width
left in between the toe road embankment and the inner edges of borrow pits or
the portion in between the top edge of road cutting and the nearest edge of
spoil banks on either side are known as berms.
