What Are Curves | Surveying Curve Types | Types of Horizontal Curves | Types of Vertical Curves |

What Are the Curves?

Curves are the gradual changes in the direction of regular bends. When curves are provided in the horizontal plane, they are referred to as horizontal curves.

When curves have some vertical elevation, they are referred to as vertical curves. Curves primarily alter the slope of the road and allow vehicles to pass through it.

Types of Curves in Surveying

Curves are the geometrical arcs used to change the gradient or the alignment. These curves are primarily of two types:

• Horizontal Curve

• Vertical Curve

What Are Horizontal Curves?

A horizontal curve is a type of curve that is used to change the alignment's direction. A flat curve is usually provided with the conjunction of the transition curve. It is primarily provided to gain access to a specific location.

Types of Horizontal Curves

Horizontal curves are classified into seven types. These seven types of curves are as follows:

1. Simple Curve

A simple curve is a type of curve produced by a single radio. This curve is most effective for large radios and slow-moving vehicles. This curve is expressed in terms of the degree of the curve.

The radius of this sort of curve is computed using the formula-

R = 1647.5/D

Where,

R= radius of the curve

D= degree of curve

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2. Compound Curve

A compound curve is a type of curve that combines two or more different radius curves to form a single curve. This curve is primarily designed to avoid the cutting-filling option.

This type of curve is highly effective to design when the road layout is aligned between a river and a cliff.

3. Reverse Curve

This type of curve is made up of two simple types of curves with oppositely varying radii. This is appropriate for crossing station yards and hilly terrain.

A deviation curve is a circular curve consisting of two reverse curves with or without a straight line. This is mainly used in accident scenes and for major track repairs on worn-out tracks.

4. Transition Curve

A transition curve has a finite radius where a vehicle enters or exits the curve. This is the primary reason for establishing a centrifugal force.

The primary purpose of this curve is to allow vehicles to maintain a proper speed while remaining safe and comfortable. A super elevation is provided to the outer track in railway tracks to maintain a proper speed while remaining safe.

5. Lemniscate Curve

The radius of this curve decreases while the Length increases.

The following equation can be used to calculate radial acceleration-

L = C√sin3h

L= length of polar ray in meter

h= polar angle in radius

C= constant

6. Spiral Curve

The length of this type of curve is proportional to the length of the traverse. This is the best type of transition curve. The rate of change of acceleration in this curve is uniform.

7. Cubic Parabolic Curve

The rate of curvature is greater than the deflection angle in this type of curve.

Here, by the equation-

Y = x3 /6RL

Y= Coordinate a point

R= Radius

L= length of the curve

What Are Vertical Curves?

Vertical curves are where a super elevation is provided for the change of gradient. Different types of topographical conditions are found in different countries, leading cause of gradient change. We also provide a vertical curve to reduce the earthwork process.

Types of Vertical Curves

There are mainly two types of vertical curves observed. They are 

• Summit Curve

• Valley Curve

1. Summit Curve

Summit curves are convex curves that have an upward convexity. The centrifugal force acts upward against gravity in this summit curve. The passengers are not bothered by this action. When we design the summit curve, we also design the overtaking and stopping sight distances separately.

2. Valley Curve

Valley curves are those with a downward convexity, sometimes called sag curves. Because the centrifugal force acts downwards in the valley curve, there is another addition of self-weight in the vehicle. An allowable rate change of centrifugal force is used to design a valley curve.

Application of Curves

Application of Horizontal Curve: A horizontal curve is the most critical element of road geometry; its primary function is to provide a smooth transition curve, which is why it is widely used in highway curves. As a result, it is the use of a horizontal curve.

Application of Vertical Curve: It is also a critical curve in road geometry. The vertical curve is commonly used in mountainous areas where the gradient of the road changes. The Hairpin bend is another application of the vertical curve.