Alignment of Road:

• Horizontal Alignment: It includes a straight line, curve etc.
• Vertical Alignment: It includes vertical or horizontal alignment.

Alignment In Design:

Basic Requirements of Ideal Alignment:

• Short.
• Easy.
• Safe.
• Economical.
• Useful.

#1. Short:

• The alignment must be as short as possible between two stations.
• This is the main reason why alignments are as straight as possible.

#2. Easy:

• Alignment should be effortless to construct and maintain, and it should be with an easy gradient and curve.

#3. Safe:

• The alignment must have safe geometric property, stable natural hill slope, cut slope, embankment, and should be safe for safe traffic operation.

#4. Economical:

• The alignment must be economical, including the initial cost, operation cost, and maintenance cost.

#5. Useful:

• The alignment should be used for maximum population place and products.

Factors Controlling Alignment:

• Obligatory Points.
• Economy.
• Geometric Design.
• Traffic.
• Other Considerations.

#1. Obligatory Points:

• Obligatory points are those points where the road alignment has to pass with the shortest distance.
• The obligatory points of a road should not pass and should be avoided when the road aligning is done.
• These points are observed between the intermediate town, bridge, mountain pass, etc.

#2. Economy:

• When we finalize the alignment of the road, then we need to consider this factor also.
• We need to take some conditions like working out the economy, initial cost, cost of maintenance, vehicle operation, etc.
• Initially, the construction cost can be decreased by selecting the cutting filling balanced alignment.

#3. Geometric Design:

• We need to consider those geometric factors like sight distance, gradient, the radius of the curve, etc.
• The alignment should be provided with adequate safe sight distance and enough overtaking sight distance.
• The new road alignment should be flat and less than the ruling gradient.
• Sometimes alignment is to be changed to adjust the alignment of the road to receive the radius of the curve.

#4. Traffic:

• Before we construct the alignment of any road, we need to study the nature of traffic of that road properly.
• From this property, we can easily find out the nature of traffic like slow-moving traffic or speedy traffic.
• In slow-moving traffic will be curling nature by joining all the villages and sharp curve but where the speed of traffic is more than we construct the straight roads with easy curves.

#5. Other Considerations:

• Other factors like hydrological factors, political considerations, monotony, drainage considerations have governed the alignment.
• The alignment should not cross foreign territory.
• To break the monotony of the long straight road, a slight bend should be provided.
• The vertical alignment guide the drainage consideration of the road.

Horizontal Alignment of Road:

• Horizontal alignment is a straight portion of the road which is connected by suitable curves.
• All the curves of roadway need a superelevation for banking of the curve, to resist vehicles from slipping, allow all the vehicle to run at a uniform speed.
• Horizontal alignment is designed on some basic rules and regulations like driver limitations, curve radius, vehicle characteristics, cost, profile, design speed, etc.

Classification of Horizontal Alignment:

• Simple Curve.
• Spiral Curve.
• Reverse Curve.
• Compound Curve.

• Horizontal alignment increases the adequate level of the user.
• Horizontal alignment secures the safety of the road user.

Vertical Alignment of Road:

• Gradient.
• Grade Compensation.
• Vertical Curve.

#1. Gradient

#a. Ruling Gradient:

• This type of gradient is the maximum gradient which is provided in the highway. It is also termed the designer gradient.
• Ruling gradient depends on terrain length, speed, power of the vehicle, etc.
• The ruling gradient in hilly terrain is difficult to provide.

#b. Exceptional Gradient:

• This type of gradient is a very exceptional gradient, and it's a very steeper gradient. The length of this gradient should not less than 100 m.

#c. Limiting Gradient:

• A limiting gradient is provided in shorter stretches on the highway.
• When limiting gradient is costlier, then we provide a limiting gradient.

#d. Minimum Gradient:

• For the drainage purpose of rainwater, the minimum gradient is required.
• For concrete drain, 1 in 500 slopes is provided, and soil drain 1 in 200 slopes is required.

#2. Grade Compensation:

• Grades which are flatter than 4%, then grade compensation is not needed.

#3. Vertical Curve:

#a. Summit Curve:

• This type of curve is a vertical curve mainly used in the upward gradient.
• If the summit curve is a parabola in shape, then it's considered as the best curve.

#b. Valley Curve:

• We provide the valley curve when the gradient is downward.
• When a vehicle entered a downward gradient, then it catches more speed, so the valley curve provides a suitable sight distance for comfort.

Highway Alignment

Alignment of Road

Alignment in Design

Horizontal Alignment Definition

Road Alignment

Vertical Alignment of Road

Road Alignment Techniques

• Geometric Design
• Topographic Surveys
• Aerial and Satellite Imagery
• Digital Terrain Models (Dtms)
• Route Optimization Software
• Environmental Considerations
• Public Input and Stakeholder Engagement

Importance of Road Alignment

• Safety
• Traffic Efficiency
• Comfort and User Experience
• Economic Benefits
• Environmental Considerations
• Future Adaptability

Road Alignment Standards

• Horizontal Alignment
• Vertical Alignment
• Cross-Section Design
• Sight Distance
• Design Speed
• Geometric Design Criteria
• Roadside Design

Road Alignment Survey

• Preliminary Study
• Reconnaissance
• Topographic Survey
• Geotechnical Investigation
• Alignment Design
• Stakeout
• As-Built Survey

Benefits of Proper Road Alignment

What Is Road Alignment?

Geometric Alignment

Horizontal and Vertical Alignment

Horizontal and Vertical Alignment of Road

Vertical Alignment in Highway Engineering

The Vertical Alignment of a Highway Includes?

The Changes in Gradient and Vertical Curve Are Covered Under Which Type of Alignment?

What Is Alignment in Surveying?

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