Question

What is the primary purpose of providing super-elevation on horizontal curves?

• A. To improve drainage
• B. To enhance aesthetics
• C. To reduce the effect of centrifugal force on vehicles
• D. To increase the speed limit on curve

Hint:

Super-elevation on horizontal curves is a critical safety feature in road design. By banking the road, it counteracts the centrifugal force, reducing the risk of skidding and improving vehicle stability, especially at higher speeds.

Answer 1

The Correct Option is C

Step 1: Identify the given data.
The question asks for the primary purpose of providing super-elevation on horizontal curves of roads. The options are:
(1) To improve drainage
(2) To enhance aesthetics
(3) To reduce the effect of centrifugal force on vehicles
(4) To increase the speed limit on curve
We need to determine the main reason for super-elevation in road design.
Step 2: Recall the concept of super-elevation.
Super-elevation (or banking) is the transverse slope provided to the road surface on horizontal curves, where the outer edge of the road is raised relative to the inner edge. This design feature is intended to help vehicles navigate curves safely by counteracting the forces acting on them.
Step 3: Analyze the purpose of super-elevation.
When a vehicle travels around a horizontal curve, it experiences a centrifugal force outward due to its motion:
\[ F_{\text{centrifugal}} = \frac{m V^2}{R} \] Where:
\( m \): Mass of the vehicle
\( V \): Speed of the vehicle
\( R \): Radius of the curve
This force tends to push the vehicle outward, potentially causing skidding or overturning. Super-elevation tilts the road such that the normal force on the vehicle provides a component inward, counteracting the centrifugal force. The super-elevation (\( e \)) is designed to balance this force, often in combination with the coefficient of lateral friction (\( f \)):
\[ e + f = \frac{V^2}{gR} \] The primary purpose of super-elevation is to reduce the effect of centrifugal force on vehicles, making it easier for them to navigate the curve safely and reducing the risk of skidding.
Step 4: Evaluate the other options.
Option 1: To improve drainage
While super-elevation does help with drainage by allowing water to flow off the road surface toward the inner edge, this is a secondary benefit, not the primary purpose.
Option 2: To enhance aesthetics
Super-elevation is a functional design feature, not primarily for aesthetic purposes.
Option 4: To increase the speed limit on curve
Super-elevation allows vehicles to navigate curves at higher speeds safely, but this is a consequence of reducing centrifugal force, not the primary purpose. The speed limit is determined by design standards, and super-elevation supports safety at those speeds.
Step 5: Select the correct option.
The primary purpose of super-elevation on horizontal curves is to reduce the effect of centrifugal force on vehicles, matching option (3).
\[ \boxed{\text{To reduce the effect of centrifugal force on vehicles}} \]