Hill roads – when are side drains required on both sides? On a hill road, side drains on both sides are essential when the roadway is located:

Introduction / Context:
Drainage design is critical for the safety and durability of hill roads. The placement of side drains depends on the road's relation to the natural hillside (cut, fill, or balanced).

Given Data / Assumptions:

• Typical two-lane hill road.
• We must select the condition that demands side drains on both sides.

Concept / Approach:
In cutting, the slope on the hill side sheds water onto the carriageway, while the cut groove itself may intercept groundwater. Drains are therefore needed both on the hill side (to intercept and carry away water) and on the valley side (to safely dispose of runoff and protect the slope/embankment).

Step-by-Step Solution:
Identify case with maximum intercepted flows → roadway in cutting.Provide a catch drain on the hill side and a side drain on the valley side.Hence, two side drains are essential in cutting.

Verification / Alternative check:
Standard hill road manuals show catch drains and lined side drains on both sides for cut sections to prevent erosion and flooding of the pavement.

Why Other Options Are Wrong:

• Spur and re-entrant curves describe plan alignment features; they do not necessarily dictate drains on both sides.
• 'None of these' is false because cutting does require both-side drainage.

Common Pitfalls:
Providing only a single side drain in cutting, which leads to water crossing the carriageway and eroding the formation.

Final Answer:
in cutting