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.