Lane,Terrain,Friction and Camber-Highway Geometric design

Basic elements of Highway Geometric design


Width of a single lane which has only one way is 3.5m

Width of single lane which has two way is 3.75m

Width of every additional lane is 3.5m

Therefor the total width of n number of lanes= 3.5* n

Intermediate carriage way

These types of carriage ways are provided usually when there is lane width needed more than single lane but less than two lanes.The lane width of intermediate carriage way is 5.5m

Terrain Classification

Terrain        Crosslope

Plain                  0-10 %

Rolling              10-25&

Mountaneous  25-60%

Steep                 Greater than 60%

Highway geometric design

Highway Cross sectional elements

Basic elements of highways are carriage way, shoulder, road margin, building margin and control lane.

Right of way =Carriage way+Shoulder+Road margin


There are two types of friction present in the road

Longitudinal Friction

Longitudinal friction is the friction aloung the longitudinal direction of the road.It can vary from 0.3 to 0.4. The friction varies with speed and breaking efficiency of the vehicle.The friction decreases with speed of the vehicle.

Lateral Friction

The lateral friction is the friction that acting aloung the transverse direction of the road.The lateral friction mainly acts when the vehicle travells in curves.The main function for this types of friction is to prevent vehicles from lateral skidiing.

The value of lateral friction is limited to 0.15

Pavement uneveness

Pavement uneveness is the average of the undulations in the surface of the road.It is represented in cm/km

The instrument used to measure pavement uneveness is bump integrator and roughometer.The acceptable value range of pavement uneveness is 150 cm/km

Camber or Cross slope

The camber or cross slope is the transverse slope given to the pavement with respect to the horizon.We talked about the longitudinal slope that is gradient.They are provided in the longitudinal direction but the camber is provided in the transverse direction.

The camber which prevents the accumulation of the water on the surface of the road.The water on the surface of the road will move towards the drainage of the side of road.

The main reason for the deterioration of roads is due to water.So the road should be designed in such a way that,whenever the water falls on the road, the water should be fastly removed.When water enters into the road, the aggregate has more affinity towards water and it absorbs water.Due to this process,the bond between aggregate and binder will reduce.This causes deterioration to the road or pavement.

Types of Camber

Parabolic camber

In parabolic camber the edges are steeper than in straight lined camber.Hence slow moving vehicle in parabolic camber has a tendency to overturn.Thus slow moving vehicles will try to occupy the central position of the parabola which will affect the overtaking of fast moving vehicles.

Straight line camber

The central portion of the straight line camber is sharp


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Grades of road


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