1. What is Sight Distance when Length of Curve is Less?

Definition: This calculator determines the minimum sight distance required when the length of the vertical curve is less than the sight distance, assuming equal height for both observer and object.

Purpose: It helps transportation engineers ensure safe visibility for drivers on vertical curves in road design.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( SD \) — Sight Distance (meters)
• \( Lc \) — Length of Curve (meters)
• \( h \) — Height of observer and object (meters)
• \( g1 \) — Upgrade gradient (%)
• \( g2 \) — Downgrade gradient (%)

Explanation: The formula combines the curve length component with a term accounting for the vertical alignment gradients.

3. Importance of Sight Distance Calculation

Details: Proper sight distance calculation ensures driver safety by providing adequate visibility to stop or maneuver, preventing accidents on vertical curves.

4. Using the Calculator

Tips: Enter the curve length, height of observer/object, and both upgrade and downgrade gradients (as percentages). Note that downgrade should be entered as a negative value.

5. Frequently Asked Questions (FAQ)

Q1: What's the typical height used for observer and object?
A: Standard values are 1.08 meters (3.5 ft) for passenger cars and 2.33 meters (7.6 ft) for trucks.

Q2: How do I enter the downgrade value?
A: Enter downgrades as negative percentages (e.g., -2.5% for a 2.5% downward slope).

Q3: When is this formula applicable?
A: This formula is used when the curve length is less than the sight distance (Lc < SD).

Q4: What if my curve length is greater than sight distance?
A: A different formula applies when Lc > SD, which doesn't include the Lc/2 term.

Q5: Why is the 400 factor used in the formula?
A: The 400 factor is a constant that incorporates unit conversions and safety factors for vertical curve calculations.

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