The basic components of the highway are the road width, cross slope, pavement, road margins, traffic separators, and curbs. These geometric elements are designed and influenced by the psychology of the driver, the characteristics of the vehicle and the traffic of the region. Highway safety is ensured by fulfilling the management of these elements in a skillful manner.

Fig.1. Cross- Section Details of a Highway in a Cutting or in an Embankment

The basic components of a highway are explained briefly with the help of figure-1 showing the highway constructed in cutting and on an embankment.

1. Cross Slope or Camber

Cross Slope or camber is the slope that is provided in the transverse direction of the pavement or carriageway, as shown in figure-1. The cross slope helps to drain off the rainwater from the road surface. Inadequate cross slope results in the flooding of water over the pavement, which results in deterioration of the highway.

The value of the slope is dependent on the type of materials used for road construction and the amount of rainfall in the region. Generally, the value of cross slope varies from 1 in 60 to 1 in 25.

2. Carriageway or Pavement

The paved portion of the highway or the road over which the traffic is meant to move is called the pavement or the carriageway. The pavement width is dependent on the width of the traffic lanes and the number of lanes planned for construction.

Traffic lane is defined as the carriageway or the pavement that is designed for the movement of one line of traffic. Generally, for single lanes with a maximum width of 2.44m, the width of the lane is desirable to have 3.75m. For the pavements designed to have two or more than two lanes, the width is supposed to be 3.5m.

3. Medians

Medians are traffic separators whose main function is to prevent the collision of the vehicles that are moving in the opposite direction on the adjacent lanes.

4. Curbs

The boundary between the pavement and the shoulder is called as curbs. Curbs are desirable to be constructed for urban roads.

Read More: Curb Features, design and Construction

5. Road Margins

Road margin includes:

  1. Shoulders
  2. Bus Bays
  3. Parking lanes
  4. Sidewalks or footpaths

Shoulders: These are provided along the road edge as shown in the figure-1 above. This area serves the purpose of accommodating vehicles that are compelled to be taken out of the pavement or the roadway. These also act as a service lane for the vehicles that have broken down.

Bus Bays: Bus bays are constructed by recessing the curb. Hence, there is no conflict with the moving traffic.

Parking Lanes: Parking lanes are provided for urban road construction hence allowing for curb parking.

Footpaths or Sidewalks: When the vehicular and pedestrian traffic is heavy, the special area is allotted for the movement of pedestrians. The area is called footpaths or sidewalks. This is provided to protect the pedestrian thus decreasing accidents.

6. Width of Roadway

The width of roadway or the width of formation is equal to the sum of the width of pavement (including the separators if any) and the shoulders.

7. Right of Way

The area of the land that acquired for the road along its alignment is termed as the right of way. Land width is defined as the width of this acquired land. The right of way is dependent on the importance of the road and the possibility of future development.

Also Read: Classification of Roads and Details