Environmental Factors

Factors like air pollution,noise pollution, flooding & landscapes also govern the designing of highways.

Following are the highway elements that are to be designed.

1. Highway Cross Sectional Element     

2. Pavement surface characteristic  

It depends on the pavement type which does depend on availability of material , cost, composition of  traffic, climatic condition & method of construction available.

Pavement surface characteristic includes

• Friction

• Unevenes

• Reflecting characteristic

• Drainage of surface water.

1. Friction/Skid resistance

• It decides the operating speed & minimum  distance required for stopping the vehicle.

• It is further classified into two:

1. Longitudinal friction.

2.  Lateral/Transverse friction.

• Maximum friction is developed when brakes are applied upto complete limit.

• Friction also governs rotation  transactional movement of a road.

• For uniform condition 

1 rotation=2piR

Rotation movement is transnational movement

• NOTE- When the path traveled along the road surface is more than the circumferential distance movements of wheels due to their rotation it is termed as “skid”.

For pure skid

  TOTAL MOVEMENT is not equal to ZERO

  ROTATIONAL MOVEMENT is equal to ZERO

When the wheel revolves more than the corresponding longitudinal movement along the road is termed as “slip”.

For pure slip

         TOTAL MOVEMENT is equal to ZERO

         ROTATIONAL MOVEMENT is not equal to ZERO

For example -

When brakes are applied to such an extent that wheels of vehicles are touched it leads to skidding & wheels of vehicles rapidly accelerate from stationary position or from slow speed on pavement which is slippery or wet or loose surface like mud.