Classification of Roads, Terms Used in Road Engineering, Alignment, Gradients & Super Elevation
Road engineering is an important branch of civil engineering that deals with the planning, design, construction, and maintenance of roads. Surveyors play a key role in road projects by providing accurate data and alignment. For ITI Surveyor trainees, understanding classification of roads, basic terms, alignment, gradients, and super elevation is essential.
Classification of Roads
Roads can be classified based on different factors:
1. Classification Based on Importance
- National Highways (NH): Connect major cities and states
- State Highways (SH): Connect important cities within a state
- District Roads: Connect towns and villages
- Village Roads: Connect rural areas
2. Classification Based on Surface
- Earthen Roads
- Gravel Roads
- Water Bound Macadam (WBM) Roads
- Bituminous Roads
- Cement Concrete Roads
3. Classification Based on Traffic
- Light Traffic Roads
- Medium Traffic Roads
- Heavy Traffic Roads
Terms Used in Road Engineering
- Formation Width: Width of road including carriageway and shoulders
- Carriageway: Portion used for vehicle movement
- Shoulder: Strip on either side of carriageway
- Camber: Cross slope for drainage
- Right of Way (ROW): Total land width reserved for road
Alignment of Roads
Alignment refers to the position or layout of the road on the ground. It includes horizontal and vertical alignment.
Factors Affecting Alignment
- Topography
- Soil condition
- Drainage
- Traffic requirement
- Economy
- Safety
Relative Importance in Road Design
1. Length of Road
Shorter length reduces cost and travel time, but must not compromise safety and design standards.
2. Height of Embankment
Embankment is raised portion of road. Excessive height increases cost and instability.
3. Depth of Cutting
Cutting is excavation below ground level. Deep cutting increases construction difficulty and cost.
4. Filling
Filling is required to raise low areas. Proper compaction is necessary for stability.
Road Gradients
Gradient is the slope of the road along its length. It is expressed as a ratio or percentage.
Types of Gradients
- Ruling Gradient: Desirable slope under normal conditions
- Limiting Gradient: Maximum permissible slope
- Exceptional Gradient: Used in difficult terrain
- Minimum Gradient: For drainage purpose
Super Elevation
Super elevation is the transverse slope provided on curves to counteract centrifugal force acting on vehicles.
Purpose
- Improves safety on curves
- Prevents skidding and overturning
- Provides comfort to passengers
Formula
e = v² / (gR)
Where:
- e = super elevation
- v = velocity of vehicle
- R = radius of curve
- g = acceleration due to gravity
Importance in Surveyor Trade
- Helps in planning and designing roads
- Ensures safe and economical construction
- Provides accurate data for alignment
Precautions
- Maintain proper gradient
- Ensure safe alignment
- Consider environmental conditions
- Use accurate survey data
Conclusion
Understanding classification of roads, basic terms, alignment, gradients, and super elevation is essential for road engineering. These concepts help in designing safe and efficient roads.
For ITI Surveyor trainees, mastering these topics is important for successful work in road construction and surveying projects.