Length of Summit Curve for Stopping Sight Distance when Curve Length is more than SSD Calculator

Formula Used:

\[ L_{Sc} = \frac{N \times SSD^2}{(\sqrt{2H} + \sqrt{2h})^2} \]

Deviation Angle (N):

Stopping Sight Distance (SSD):

meters

Height of Eye Level (H):

meters

Height of Subject (h):

meters

Length of Summit Curve (L_Sc): meters

1. What is Length of Summit Curve for Stopping Sight Distance?

Definition: This calculator determines the minimum length of a parabolic summit curve needed to provide adequate stopping sight distance when the curve length is greater than the stopping sight distance.

Purpose: It helps highway engineers design safe vertical curves that ensure drivers have sufficient visibility to stop safely.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ L_{Sc} = \frac{N \times SSD^2}{(\sqrt{2H} + \sqrt{2h})^2} \]

Where:

\( L_{Sc} \) — Length of summit curve (meters)
\( N \) — Deviation angle (algebraic difference in grades, as decimal)
\( SSD \) — Stopping sight distance (meters)
\( H \) — Height of eye level of driver above roadway (meters, default 1.2m)
\( h \) — Height of subject above pavement surface (meters, default 0.15m)

Explanation: The formula calculates the curve length needed to ensure a driver can see an object on the road with enough distance to stop safely.

3. Importance of Summit Curve Calculation

Details: Proper summit curve design prevents accidents by ensuring drivers have adequate visibility over hills and crests, especially important for high-speed roads.

4. Using the Calculator

Tips:

Enter deviation angle as a percentage (e.g., 5% grade change = 5)
Typical eye height (H): 1.2 meters (4 feet)
Typical object height (h): 0.15 meters (6 inches)
All values must be positive numbers

5. Frequently Asked Questions (FAQ)

Q1: Why is the deviation angle input as percentage?
A: Highway grades are typically expressed as percentages (e.g., 5% grade). The calculator automatically converts this to decimal for the calculation.

Q2: What's the difference when curve length is less than SSD?
A: A different formula applies when the curve length is shorter than the stopping sight distance (L < SSD).

Q3: How does height affect the calculation?
A: Higher eye level or object height increases visibility, potentially allowing shorter curves for the same SSD.

Q4: What are typical SSD values?
A: SSD varies by design speed - from about 60m (20mph) to 250m (80mph) for highways.

Q5: When would I use this calculator?
A: For designing vertical curves on roads where the curve length will be longer than the required stopping sight distance.