Roads

ROADS

 

1. ADVANTAGES OF ROADS

Of the four transportation systems, roads are the most important system due to following reasons:

1. Roads are essential for the economic development of a country. For speedy transportation of commodities, a good network of roads is essential.

2. Of all the modes of transport, road transport is nearest and at the easiest approach of people. People and goods have to be first moved by road, before reaching other modes of transport.

3. Roads connect all places, hills to tiny villages.

4. National Highways have nowadays become a symbol of prosperity of a country. A goo system of roads helps the growth of trade all over the country.

5. A good network of roads enables villagers to transport their commodities to the market speedily and easily.

6. During emergencies such as accidents, the injured person can be rushed immediately (during the Golden Hour) to a hospital through a good system of roads.

7. During floods and droughts, the basic commodities can be efficiently rushed from the other parts of the country through a good system of roads.

8. An efficient system of roads helps in carrying out exploration works at the remotest places, which are otherwise difficult to reach. 9. Better law and order can be maintained in the society.

 

2. ROAD TRANSPORT CHARACTERISTICS

1. Roads can be used by all kinds of vehicles such as lorries, buses, cars, two-wheelers, etc.

2. Roads are equally useful for pedestrians.

3. Railways will lead to railway stations, aero-planes to airports and ships to harbours. But, roads can reach any place.

 4. Local communication among villages, villages and towns is possible only through roads. Other modes of transport cannot go from village to village.

5. Movements on roads are not time-bound as in the case of railways, waterways and airways.

 

3. CROSS-SECTION DETAILS OF A ROAD

Fig. 1 shows the cross-section details of a road. The details are:

1. Roadway or Road Formation: Roadway is the portion of the road used for traffic. It includes Carriageway and Shoulders.

2. Carriageway or Width of Pavement: It is the specific portion of the road meant for only the vehicular movement. Carriageway is also known as Width of Pavement. Multilane carriage ways have a width of 3.75 m per lane. The width of carriageway of village roads may be limited to 3 m.

Surface Characteristics: The pavement surface depends on the material used for the construction of the road surface. The important surface characteristics of the pavement are the friction, unevenness, light reflecting properties and drainage of surface water.

3. Camber: Camber is the rise given at the center of the carriageway of a road. The top surface of the carriageway is provided with a slope in the transverse direction so that rain water turns-off smoothly. It depends on  (i) the nature of the surface of the carriage way and

(ii) the intensity of rainfall in the region.

4. Shoulder: It is the portion of the road between the edge of the carriageway and the edge of the Road Formation. Shoulder accommodates cycle track, footpath, road signs, electric/telegraphic posts, etc. The vehicles use shoulders while overtaking or crossing.

5. Right-of-way and Land Width: It is the area of land procured and reserved for the widening of the roadway and development of roads. It denotes the special right or privilege of use of a way obtained by traffic bye-law. Land Width is the width of the land acquired.

Gradient: The longitudinal slope of the road is known as Gradient. It is necessary for rainwater drainage and should match the ground profile.

Vertical Curve: When gradients change in the alignment of the road, the Vertical Curve is. provided to join the two gradients.

Horizontal Curve: Whenever the ground alignment changes direction in plan, the two straight alignments are connected by a Horizontal Curve of a large radius.

Sight Distance: It is defined as the length of the road visible ahead to a driver at any instance. The drivers of two vehicles in a road approaching from the opposite ends of a vertical or horizontal curve should have a clear vision of the vehicle from the other end. The minimum sight distance should be the distance needed for stopping the vehicle.

Super Elevation: It is defined as the inward transverse inclination given to the cross-section of the carriageway at places where the road is curved horizontally. Fig. 2 shows the super elevation provided to the carriage way.

When a vehicle negotiates a horizontal curve, it is subjected to the action of centrifugal force. Super elevation counteracts the effect due to this force.

Purposes of Super Elevation

1. Super Elevation counteracts the effect due to centrifugal force that tends to push the moving vehicle outward at a horizontal curve.

2. It enables the fast moving vehicles to negotiate the curve safely without skidding or overturning.

3. Also, it provides drainage to the entire width of the road towards the inner side.

 

4. STRUCTURE OF A ROAD

Structure of a Road generally consists of:

1. Wearing Surface: Wearing Surface resists wear and tear due to traffic. It gives a smooth riding surface. In Flexible Pavements, a bituminous surface is used as wearing surface. In Rigid Pavements, cement concrete acts both as wearing course and base course.

2. Base Course: It is a layer placed between the wearing surface and sub-base course. It gives firm support to the road surface and transmits the wheel load to the underlying layer.

3. Sub-base Course: It is an additional layer between the base course and the soil sub-grade. It is provided to improve the load supporting capacity of the soil by distributing the load.

4. Soil Sub-grade: The top of the earth is filled with soil sub-grade and well compacted.