The point where the alignment changes from a straight line or tangent to a circular curve is called as-
Point of curvature
Understanding Highway Curve Alignment
Highway alignment involves the layout of the center line of the road on the ground. It consists of straight lines (tangents) and curves (horizontal and vertical) connecting them. Smooth transitions between straight sections and curves are crucial for safe and comfortable driving.
When a straight section of a road needs to change direction, a horizontal curve is introduced. This curve allows vehicles to gradually change direction rather than making a sharp turn. The points where the straight sections connect with the curve have specific names in civil engineering and highway design.
Key Points on a Horizontal Circular Curve
A simple horizontal circular curve connecting two tangents has specific points that define its start and end. These points are essential for surveying and laying out the curve on the ground.
- Tangent: The straight section of the road alignment before or after a curve.
- Circular Curve: The curved section connecting two tangents, usually a segment of a circle.
The transition from a straight line to a circular curve happens at a specific point. Similarly, the transition from the circular curve back to another straight line happens at another specific point.
Analyzing the Options for Alignment Change Points
Let's examine the given options related to the points on a circular curve in highway alignment:
- Point of commencement: This is a general term and doesn't specifically refer to the start of a circular curve from a tangent in highway design context.
- Point of curvature: This is the point where the alignment changes from a straight line (tangent) to the circular curve. It marks the beginning of the curve. It is often denoted as PC or BC (Beginning of Curve) or TC (Tangent to Curve).
- Point of tangency: This is the point where the circular curve ends and connects back to the next straight line (tangent). It marks the end of the curve. It is often denoted as PT or EC (End of Curve) or CT (Curve to Tangent).
- Finishing mark: This term is not standard terminology used to describe a point on a highway horizontal curve alignment. It might refer to a construction marker but not a specific geometric point defining the curve limits.
The question asks for the point where the alignment changes from a straight line or tangent to a circular curve. Based on the standard terminology in highway design, this specific point is known as the Point of Curvature.
Identifying the Point of Curvature
Consider a simple horizontal curve layout:
Tangent 1 → Circular Curve → Tangent 2
The point where Tangent 1 meets the beginning of the Circular Curve is the Point of Curvature (PC).
The point where the end of the Circular Curve meets Tangent 2 is the Point of Tangency (PT).
Therefore, the point where the transition from a straight line or tangent to a circular curve occurs is the Point of Curvature.
| Point | Description | Denotation |
|---|---|---|
| Point of Curvature | Where tangent meets the beginning of the curve | PC (or BC, TC) |
| Point of Tangency | Where the end of the curve meets tangent | PT (or EC, CT) |
| Point of Intersection | Where the two tangents would meet if extended | PI (or V - Vertex) |
Revision Table: Highway Alignment Points
| Term | Definition Relevant to Highway Curves |
|---|---|
| Point of Curvature (PC) | The point where the alignment transitions from a tangent (straight line) to a circular curve. |
| Point of Tangency (PT) | The point where the alignment transitions from a circular curve to a tangent (straight line). |
| Tangent | A straight section of the highway alignment. |
| Circular Curve | A curved section of the highway alignment, typically a segment of a circle, connecting two tangents. |
Additional Information on Highway Curve Layout
Understanding the points on a highway curve is fundamental to its layout and design. Apart from the Point of Curvature (PC) and Point of Tangency (PT), another important point is the Point of Intersection (PI) or Vertex (V), which is the theoretical point where the two tangents intersect if extended. The distance from PI to PC or PI to PT along the tangent is called the tangent length. The radius of the curve (R) is a key parameter determining the sharpness of the curve and influences the design speed and superelevation.
Modern highway design often incorporates transition curves (like spiral curves) between the tangent and the circular curve to provide a more gradual change in curvature and superelevation, enhancing comfort and safety. In such cases, the points marking the start and end of the transition curves become important (e.g., Tangent-to-Spiral TS, Spiral-to-Curve SC, Curve-to-Spiral CS, Spiral-to-Tangent ST).
Important Questions from Curves
The difference in length between the arc and the subtended chord on the earth's surface is taken as 500mm in:
The length of a simple circular curve of radius R meters and deflection angle D degrees will be
The angle of intersection of a curve is the angle between the
The shift of a circular curve is given by __________
Where,
L = Length of transition curve and R = Radius of the circular curve
A curve which consists of a two circular arcs of same or different radii having their centers to the different sides of the common tangent is called a________.
