Alignment of Road | Alignment In Design | Horizontal Alignment of Road | Vertical Alignment of Road

Alignment of Road

Alignment of Road:

Alignment is the centre line position of highway on the ground; it is also termed as highway alignment.

The alignment guides the good pass of the road through wright Alignment, which is the most economical and easy to construct.

There are mainly two types of alignment-

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

Alignment is a series of points, lines, curves etc. To construct a road, we need to locate those points properly.

Centreline of a road follows the horizontal alignment and vertical gradient follows the vertical gradient.

Also, Read: What Are Plastic Roads | How to Make Plastic Roads | Who Invented Plastic Roads | First Man Made Plastic Road | Advantages & Disadvantages of Plastic Roads

Alignment In Design:

Alignment Road In Design

Basic Requirements of Ideal Alignment:

The basic requirements of an ideal configuration are as follows.

  • 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.

Also, Read: What Is Road Pattern | Different Types of Road Patterns | Grid Pattern Definition | Radial Pattern | Rectangular or Block Pattern | Minimum Travel Pattern

Factors Controlling Alignment:

The basic requirements of an ideal configuration are as follows.

  • 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.

Also, Read: WBM Road | Material Required for Construction of WBM Road | Construction Procedure of WBM Road | Advantages & Disadvantages of WBM Road

Horizontal Alignment of 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.

Also, Read: What Is a Classified Road | Classification of Roads in India

Classification of Horizontal Alignment:

There are mainly four types of classification are observed, those are-

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

An object of Horizontal Alignment:

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

Vertical Alignment of Road:

Vertical Alignment of Road

Vertical alignment of the road comprises of gradients and vertical curve. Vertical alignment is defined as the height and depth in a vertical axis with respect to the horizontal axis, this height and depth, it creates a gradient and vertical curve.

Vertical alignment of roadway consists of the following factors-

  • Gradient.
  • Grade Compensation.
  • Vertical Curve.

Also, Read: What Is Superelevation | Superelevation Definition | Superelevation Formula | Calculation of Superelevation in Roads

#1. Gradient

Gradient of Road

The gradient is rise and fall of the gradient with respect to the horizontal line.

Gradients are mainly four types those are-

#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.

Also, Read: Road Development Plans in India

#2. Grade Compensation:

Grade Compensation

When the horizontal curve lies in a vertical curve, then there is resistance is created by a circular curve.

IRC specifications for grade compensation-

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

#3. Vertical Curve:

vertical curve

There are mainly two types of vertical curves are exist, they are-

#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.

Also, Read: What Is the Gradient of Road | Types of Road Gradient | Factors Affecting Gradient |Effect of Gradient on Roads


Short Note

Highway Alignment

Highway Alignment is the position or layout of the centre line of the highway on the ground is called the alignment. It includes a straight path, horizontal deviation, and curves.

Alignment of Road

It is the direction through which the road will pass. Road alignment provides proper guidance to pass the road through the alignment, which is most economical, easy to construct, and free from conflicts. There are two types of road alignment. It includes straight stretches, curves, etc.

Alignment in Design

Alignment is a design principle that refers to lining up text or graphics on a page. A design with poor alignment will look cluttered and unfinished. But aligning elements on the page will organize your design and make it easier to read.

Horizontal Alignment Definition

The horizontal alignment is the route of the road, defined geometrically as a series of horizontal tangents (straight roadway sections), circular curves, and spiral transitions. It shows the proposed roadway location in relation to the existing terrain and adjacent land conditions.

Road Alignment

Road alignment is the positioning of the centerline of the highway or road. It is also called as highway alignment. Simply, it is the direction through which the road will pass. Road alignment provides a proper guidance to pass the road through the alignment which is most economical, easy to construct and free from conflicts.

Vertical Alignment of Road

The vertical alignment of a road consists of gradients(straight lines in a vertical plane) and vertical curves. The vertical alignment is usually drawn as a profile, which is a graph with elevation as a vertical axis and the horizontal distance along the centre line of the road as the horizontal axis.

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