Length of Summit Curve when Length of Curve is less than OSD or ISD Calculator

Formula:

\[ L_{Sc} = 2 \times SSD - \left( \frac{8 \times H}{N} \right) \]

Length of Parabolic Summit Curve (L_Sc): m

1. What is Length of Summit Curve when Length of Curve is less than OSD or ISD?

Definition: This calculator determines the length of a parabolic summit curve (vertical curve with upward gradient) when the curve length is less than the overtaking sight distance (OSD) or intermediate sight distance (ISD).

Purpose: It helps highway engineers design safe vertical curves that provide adequate stopping sight distance for drivers.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L_{Sc} = 2 \times SSD - \left( \frac{8 \times H}{N} \right) \]

Where:

\( L_{Sc} \) — Length of parabolic summit curve (meters)
\( SSD \) — Stopping sight distance (meters)
\( H \) — Height of eye level of driver above roadway surface (meters, typically 1.2m)
\( N \) — Deviation angle (algebraic difference in grades, ±5%)

Explanation: The formula calculates the minimum curve length needed to provide the required stopping sight distance considering driver eye height and grade changes.

3. Importance of Summit Curve Calculation

Details: Proper summit curve design ensures driver safety by maintaining visibility over crest vertical curves, preventing accidents caused by limited sight distance.

4. Using the Calculator

Tips: Enter the stopping sight distance (SSD) in meters, height of eye level (default 1.2m), and deviation angle (default 0.08 for ±5% grade). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical eye height (H) value?
A: The standard value is 1.2 meters, representing the average eye height of a truck driver.

Q2: How is deviation angle (N) determined?
A: It's the algebraic difference between the incoming and outgoing grades (e.g., +3% to -2% would be N = 0.05).

Q3: When is this formula applicable?
A: When the calculated curve length is less than the overtaking sight distance (OSD) or intermediate sight distance (ISD).

Q4: What if my curve length is greater than OSD or ISD?
A: A different formula should be used that accounts for the longer distance requirements.

Q5: Why is stopping sight distance important?
A: It's the distance needed for a driver to see an obstacle and safely stop before reaching it.