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

Length of Summit Curve Formula:

\[ L_{Sc} = \frac{N \times SSD^2}{8 \times H} \]

Length of Summit Curve (L_Sc): meters

1. What is Length of Summit Curve?

Definition: The length of summit curve is the vertical curve with a gradient upwards, designed for proper visibility when the curve length is greater than OSD (Overtaking Sight Distance) or ISD (Intermediate Sight Distance).

Purpose: It ensures safe stopping sight distance for drivers when approaching a summit or crest in the road.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L_{Sc} = \frac{N \times SSD^2}{8 \times H} \]

Where:

\( L_{Sc} \) — Length of summit curve (meters)
\( N \) — Deviation angle (algebraic difference in grades) in percentage
\( SSD \) — Stopping sight distance (meters)
\( H \) — Height of eye level of driver above roadway surface (meters)

Explanation: The formula calculates the minimum length of vertical curve needed to provide adequate stopping sight distance.

3. Importance of Summit Curve Calculation

Details: Proper summit curve length ensures driver safety by providing sufficient visibility to stop safely when approaching a crest vertical curve.

4. Using the Calculator

Tips: Enter the deviation angle (N) in percentage, stopping sight distance (SSD) in meters, and height of eye level (H) in meters (default 1.2m). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical height for driver's eye level?
A: The standard height is 1.2 meters (approximately 4 feet) for passenger vehicles.

Q2: How is deviation angle (N) determined?
A: It's the algebraic difference between the approaching and departing grades (e.g., +3% to -2% would be N = 5%).

Q3: What's the difference between SSD, OSD and ISD?
A: SSD is stopping sight distance, OSD is overtaking sight distance, and ISD is intermediate sight distance (2*SSD).

Q4: When is this formula applicable?
A: This formula is used when the calculated curve length is greater than both OSD and ISD.

Q5: What if my curve length is less than SSD?
A: A different formula (L = 2*SSD - (8*H)/N) should be used when L < SSD.