Components of Road pavement structure – Parts of a road and functions

Components of a road or parts of a road plays an important part in ensuring the safety and service life of a road. Components of a road is designed to meet the design requirements, functional requirements etc. This article is about the components of road/parts of a road and its functions.

COMPONENTS OF A ROAD
COMPONENTS OF A ROAD

Also read : Classification of road – Full details

Also read : Alignment of road – Factors affecting – obligatory points

Components of a Road

  • Carriage way or pavement
  • Road way or formation width
  • Camber or cross slope
  • Kerbs
  • Medians
  • Road margins
  • Right of way ( ROW)
Video on components of a road

Carriage way or pavement width

The paved portion or surface of the road for traffic movement without any restriction is called the carriageway. The width of the carriageway/ pavement width depends on the number of traffic lanes. The number of lines is decided based on the type of road, service importance, and traffic density.

The carriageway is divided into a single carriageway and a dual carriageway as shown in the figure.

SINGLE CARRIAGE WAY AND DUAL CARRIAGE WAY
SINGLE CARRIAGE WAY AND DUAL CARRIAGE WAY

The maximum permissible width of a vehicle is 2.44 and the side clearance for single lane traffic is 0.68 m. The required minimum lane width is 3.75 m for a single lane road. For the dual carriageway, the pavement width is two times 3.75 mtr. ie: 7.5 mtr.

Each country has its own specification for carriage way widths.

Must read : Road pavement layers – Components and function

Carriage width as per IRC

CARRIAGE WIDTH
CARRIAGE WIDTH

Road way or formation width

Width of formation or roadway width is the sum of the widths of pavements or carriage way including separators and shoulders. This does not include the extra land in formation/cutting. (Ref : Diagram)

Camber or cross slope

Camber or cross slope provided to raise the middle of the road in the transverse direction to drain of water. Inadequate slopes result in flooding of water on the pavement which may deteriorate the surface in course of time. The too steep slope is undesirable for it will erode the surface.

CAMBER TYPES
CAMBER TYPES

Camber or cross slope serves as Surface protection especially for gravel and bituminous roads. They protect the sub grade by providing proper drainage and enables quick drying of pavement which in turn protects the vehicles from slipping and thereby increases safety.

DUAL CARRIAGE WAY
DUAL CARRIAGE WAY

The value of camber depends on the type of material used for making it and rainfall density in that region.

Kerbs

Kerbs are dividing line between carriage way and shoulders, footpath or islands. The following are the different types of kerbs.

Low or mountable kerbs allows the vehicle to enter the shoulder area with little difficultly. Height of 10 cm above pavement level & Edge will have a slope allowing vehicle to step over easily.

Semi barrier type kerbs are used when the pedestrian traffic is high. Their height is 15 cm above the pavement edge. This type of kerb prevents encroachment of parking vehicles, but at acute emergency it is possible to drive over this kerb with some difficulty.

Barrier type kerbs are designed to discourage vehicles from leaving the pavement. 

Submerged kerbs are used in rural roads as edges between the pavement edge and shoulders. 

Function of kerb

  • Drainage control
  • Demarking of walkways
  • Roadway demarking
  • Maintenance assistant
  • Assisting road side development.

Medians or traffic seperators

ROAD SEPARATED WITH MEDIANS
ROAD SEPARATED WITH MEDIANS

They are physical or painted separation provided to separate two road ways. Mainly used to differentiate vehicles based on speed.

Right of way

Right of way or ROW is the land to be acquired for the road along its alignment. The right of way depends on the importance of the road, traffic an possibility of expansion in the future. They include the total elements of the road like carriageway, shoulders, drainage system, cuttings, and embankment slopes, etc.

Factors influencing the width of ROW

a) Width of formation

b) Embankment depth and cutting depth

c) Side slopes of embankment or cutting

d) Drainage system

e) site distance considerations

f) Future widening & Service roads.

Road margins

The portion of the road beyond the carriageway and on the roadway can be generally called road margin. Various elements that form the road margins are given below.

They include

  • shoulders
  • Parking lines
  • Bus bay
  • Service roads
  • Cycle track
  • Footpath
  • Guard rail

For more details about road margin : Must Read

Road margins- 6 types of road margins in highway

7 thoughts on “Components of Road pavement structure – Parts of a road and functions

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