# Types of curves

|Table of Contents

**Types of curves**

Curves are provided whenever a change direction of the road is from right to another side (vice versa) or changes the road alignment from up to down or down to up (vice versa). Curves are a critical element in the road pavement design. Curves are provided with a maximum speed limit that should lie very strictly. Following the speed limit becomes essential as the exceed in speed may lead to the chances of the vehicle becoming out of control thus increasing the odds of fatal accidents and while negotiating a turn.

Also, curve design is very necessary that appropriate safety measures be adopted at all vertical curves and horizontal curves to decrease the risks of hazardous circumstances and make the infrastructure road user friendly.

The low-cost safety measures that can be adopted at curves included information signs, delineators, flexible posts, rumble strips, pavement markings, fluorescent strips, road safety barriers, etc.

### Types of Curves

Mainly two types of curves provided primarily for the comfort and ease of the motorists in the road namely:

- Horizontal Curve

- Vertical Curve

**Horizontal Curves in Surveying**

Horizontal curves are provided to change the alignment or the direction of a road. Horizontal Curves are circular arcs or circular curves. The sharpness of a curve increases as the radius is decreased which makes it dangerous and risky.

**Terminologies in Simple Curve**

**Point of curvature**

Point of curvature. It is the starting of a curve.

2.** Point of tangency**

Point of tangency. It is the last point of the curve.

3. **Point of the intersection.**

it is also called vertex point, Point of the intersection of the tangents.

4. **Length of tangent**

Length of a tangent from Point curvature to Point of intersection and from Point of the intersection to Point of tangency. It is known as a subtangent.

5. **Radius of curve **

The radius of the curve, or simply the radius of the curve.

6. **Length of chord**

Length of the chord from Point of curvature to point of tangency. Point Q as shown below is the midpoint of (L) Length of the chord.

7. **Length of a curve**

Length of the curve from Point of curvature to point of tangency. Point M in the figure is the midpoint of the length of the curve.

8. **External distance**

External distance, the nearest distance from Point of the intersection to the curve.

9.** Middle ordinate**

Middle ordinate, the distance between the midpoint of the curve to the midpoint of the chord.

10. **Deflection angle**

Deflection angle (also called central angle and angle of intersection). The deflection angle is the angle of the intersection of the tangents. The angle subtended by Point of curvature and Point of tangency at O is also equal to (I) Deflection angle, where O is the center of the circular curve from the above figure.

11. **offset distance**

offset distance from tangent to the curve. Note: x is perpendicular to the length of a tangent.

12.** offset angle **

offset angle subtended at Point of curvature between the Point of intersection and any point in the curve.

13. **Degree of the curve.**

Degree of the curve. The degree of the curve is the central angle subtended by a length of curve equal to one station. In SI, one station is equal to 20 m and In the English system, one station is equal to 100 ft.

14. **Sub chord **

distance between two adjacent full stations points.

**Types of Horizontal Curve:**

**Simple Curve:**

A simple arc provided in the road to impose a curve between the two straight lines of roads.

**Compound Curve:**

Combination of two simple curves of roads combined together to curve in the same direction.

**Reverse Curve:**

Two simple curves of Combination combined together to curve in the equal direction.

**Transition or Spiral Curve:**

A Spiral Curve that has a varying radius. Spiral Curve provided with a between the simple curves in a compound curve and a simple curve.

While the vehicle is turning it is exposed to two forces. The first force ground is gravity which attracts the vehicle towards. The second is which is an external force required to keep the vehicle on a curved path of centripetal force. At any velocity, the centripetal force would be greater for a smaller (tighter turn) radius than a larger radius (broader one). Thus, the vehicle would have to make a very large circle in order to negotiate a turn.

is defined as superelevation at This phenomenon, which is the amount of rising seen on a given cross-section of a turning road, spiral curve is otherwise known as a slope.

**Vertical Curves in Civil Engineering Surveying**

they are provided to change the slope in the road carriageway and may or may not be symmetrical. Vertical curves are not circular and parabolic like horizontal curves. Identifying the safe passing sight distance and the proper grade is the main design criterion of the vertical curve, crest vertical curve the length should be enough to provide in sag vertical curve and safe stopping sight distance the length is important as it influences the factors such as drainage requirements and rider comfort, headlight sight distance.

**Types of Vertical Curve:**

**Sag Curve**

They are those which change the alignment of the road from uphill to downhill on the hill areas.

**Crest Curve/Summit Curve**

They are those which change the alignment of the road from downhill to uphill on the hill areas. crest vertical curves designed it is important that the grades are not too high which makes it difficult for the driver to travel upon it.