Set Back Distance by Approx Method (L is less than S) Calculator

Set Back Distance Formula:

\[ m = \frac{L_c \times (2 \times SSD - L_c)}{8 \times R_t} \]

Set Back Distance (m):

1. What is Set Back Distance by Approx Method?

Definition: Set back distance is the distance required from the centerline of a horizontal curve to an obstruction on the inner side of the curve to provide adequate sight distance at a horizontal curve.

Purpose: It ensures proper visibility and safety for vehicles navigating horizontal curves, especially when the curve length is less than the stopping sight distance.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ m = \frac{L_c \times (2 \times SSD - L_c)}{8 \times R_t} \]

Where:

\( m \) — Set back distance (meters)
\( L_c \) — Length of curve (meters)
\( SSD \) — Stopping sight distance (meters)
\( R_t \) — Radius of curve (meters)

Note: This formula applies when the length of curve (L_c) is less than the stopping sight distance (SSD).

3. Importance of Set Back Distance Calculation

Details: Proper set back distance calculation ensures:

Safe stopping sight distance for vehicles
Clearance from roadside obstructions
Compliance with road design standards
Reduced accident risk on curves

4. Using the Calculator

Tips:

Enter all values in meters
All values must be positive numbers
The ±5% indicates the typical tolerance range for these measurements
Ensure L_c < SSD for this approximation method

5. Frequently Asked Questions (FAQ)

Q1: When should I use this approximate method?
A: Use this method when the length of curve is less than the stopping sight distance (L_c < SSD).

Q2: What if my curve length is greater than SSD?
A: A different formula should be used when L_c > SSD.

Q3: What factors affect stopping sight distance?
A: SSD depends on design speed, driver reaction time, road gradient, and friction factor.

Q4: How is radius of curve determined?
A: It's typically determined by design speed, superelevation, and side friction factors.

Q5: Why is there a ±5% tolerance?
A: This accounts for measurement uncertainties and practical construction tolerances.