How to find out the exact size of carriage way or pavement
This exclusive civil engineering article teaches you how to define the exact size of carriage way or pavement.
A carriageway or a roadway comprises of a breadth of road over which there is no obstruction with any physical barriers or separation for any vehicle to transit parallel.
The breadth of the carriage way is based on the breadth of the traffic lane as well as the number of lanes. Likewise the breadth of traffic lane is relied upon the breadth of the vehicle and the clearance at sides and at the center of the road way, since the side and center clearance significantly makes the operating speed and safety of road traffic better.
It should be kept in mind that with adherence to IRC specifications for carriage way breadth, the maximum allowable breadth of a vehicle should be 2.44m. The acceptable side clearance for single lane traffic is 0.68 meters. By summing up these three perimeters, the desired minimum lane width should be 3.8 meters that is usually chosen as 3.75 meters for a single lane road. Therefore, for a single lane road, the least road breadth should be 3.75 meters.
But, it can vary for a two lane road. For two lane road, the necessary side clearance should be approx 0.53 meters on both sides and 1.06 meters in the center. So, a two lane road, minimum of 3.5 meters should be needed for each lane.
With adherence to IRC, the carriage way breadth for various types of lanes should be as follow:-
| Type of carriage way | Width of carriage way |
|---|---|
| Single lane road | 3.75 |
| Two lane, exclusive of kerbs | 7.0 |
| Two lanes, elevated kerbs | 7.5 |
| Intermediate carriage | 5.5 |
| Multi-lane | 3.5 |
The above values for carriage way breadth will be applicable if the road or highway remains in straight line.
In case, there are no horizontal curves in road or highway, additional width of pavement should be provided.
On horizontal curves having radius up to 300 meter, breadth of pavement and roadway should be raised according to the following table derived from IRC specifications :-
| Radius of curve | Additional Width |
|---|---|
| Upto 40 m | 1.5 m |
| 41 to 60 m | 1.2 m |
| 61-100 m | 0.9 m |
| 101-300 m | 0.6 m |
Curve Widening:-
Curve widening means the additional expansion of carriage way at curves arranged horizontally. The value of the additional expansion is generally based on the length of the vehicle, design speed and radius of the horizontal curve. To workout the expansion of certain curve, the formula given below is recommended.
Expansion because of psychological impact.
Ws = V / 9.5√R
Expansion because of mechanical impact
Wm = nL2 / 2R
Therefore, total expansion = W = Ws + Wm
