To prevent overturning of bullock carts on curves, the Indian Roads Congress (IRC) recommends a maximum super-elevation of:

Introduction / Context:
Super-elevation (cant) is the transverse slope provided on horizontal curves to counteract the centrifugal force. In mixed traffic conditions with slow-moving vehicles such as bullock carts, excessive super-elevation can cause instability and risk overturning.

Given Data / Assumptions:

• Mixed traffic including animal-drawn vehicles.
• Conservative design to enhance safety at low speeds.
• We seek the upper limit recommended to avoid overturning.

Concept / Approach:
Super-elevation e is selected to balance a portion of centrifugal force: e + f = v^2/(225R) (v in km/h, R in m). For slow vehicles with high centers of gravity and lower lateral grip, a high e is undesirable. Hence a cap is specified.

Step-by-Step Solution:
Recognize that for mixed traffic with bullock carts, the IRC limits maximum e.The common cap used is e_max = 1 in 15 (about 6.7%).Therefore, choose 1 in 15 as the correct option.

Verification / Alternative check:
Many standard references cite a practical upper bound near 1 in 15 for such mixed-traffic roads, keeping roll tendencies within safe limits while offering some counter to centrifugal action.

Why Other Options Are Wrong:

• 1 in 10 or 1 in 12: too steep for animal-drawn carts, increases overturning tendency.
• 1 in 20 and 1 in 25: conservative but may be insufficient on sharper curves; the question seeks the recommended maximum limit.

Common Pitfalls:

• Applying high-speed super-elevation caps to low-speed mixed traffic context.
• Ignoring the effect of high center of gravity and narrow wheel track of carts.

Final Answer:
1 in 15