Noise abatement by green belts By approximately how many decibels can planting dense tree belts (e.g., coconut, neem) near hospitals and schools reduce ambient noise levels under practical conditions?

Introduction / Context:
Green belts act as physical and psychological buffers against urban noise. Vegetation can scatter, absorb, and block sound, though its effect depends on belt width, foliage density, frequency spectrum of noise, and ground conditions. Urban planners commonly deploy trees and shrubs near sensitive receptors such as hospitals and schools to mitigate noise nuisance.

Given Data / Assumptions:

• Moderate-width belts with mixed species and full foliage.
• Noise sources include road traffic and typical urban activities.
• Measurement positions are just behind the vegetative barrier relative to the source.

Concept / Approach:
Vegetation reduces sound primarily by high-frequency scattering and some absorption; low-frequency traffic noise penetrates more easily. Practical guidance suggests that well-designed belts (10–30 m wide, dense undergrowth) achieve reductions around 5–10 dB at receiver locations close to the barrier, with diminishing returns beyond certain widths or in the presence of gaps.

Step-by-Step Solution:

Verification / Alternative check:
Field studies and standards handbooks report 5–10 dB(A) attenuation for dense plantings; higher claims usually require engineered barriers (e.g., walls, earth berms).

Why Other Options Are Wrong:

• 1–2 dB: Too small for dense green belts.
• 15–20 dB or 25–30 dB: Typically require solid barriers or substantial berms.
• 35–40 dB: Unrealistic for vegetation alone.

Common Pitfalls:
Overestimating tree-only performance; ignoring gaps or seasonal leaf loss which reduce effectiveness.

Final Answer:
5-10