Treated and untreated road shoulders | Why shoulders are provided ?

Road shoulders

They may be defined as

Strips parallel along with the carriage way on both sides are known as road shoulders.

Or 

The part of roadway outside of the traveled way on either edge of a road way.

Types of Shoulders

Treated shoulders

The shoulders which are mostly having the same material as that of the carriage way.

1. Treated road shoulders save little economy as the material is almost same as that of the carriage way. Not of same quality as that of carriage way.
2. Sometimes bricks are used as a shoulder material.
3. In case of treated shoulders, 3-4 inch material of the base course is recommended.

Untreated shoulders

The shoulders which are simply the normal soil surface are untreated shoulders.

1. These shoulders are very economical.
2. Mostly used for rural areas transportation system.
3. In case of untreated shoulders, 3-4 inch base course layer is not provided. Thus it saves economy.

Why shoulders are provided ?

Road shoulders are provided because:

1. They provide lateral stability to the carriage way.
2. When they are well maintained, they increase the width of the existing carriage way.
3. In case of emergency, shoulders are helpful in parking.
4. In case of emergency overtaking, well maintained road shoulders are helpful.
5. They help in future widening of the road.