Mitigation Measures

Noise Barrier/Enclosure

Noise Barrier

A noise barrier or acoustic shield reduces noise by interrupting the propagation of sound waves. With proper design and selection of material for the noise barrier or acoustic shield, noise reaching a noise sensitive receiver would be primarily through diffraction over the top of the barrier and around its ends.

The acoustical "shadow zone" created behind the barrier is where noise levels are substantially lowered.

To function well, the barrier must prevent the line-of-sight between the noise source and the receiver.

Effective noise barriers can reduce noise levels by as much as 20 dB(A).

The following are some common types of noise barriers used in Hong Kong. Please click on the demo button to read the details. Then click on the stop button to stop the sound/demo.

(a) Vertical Barrier

(b) Cantilever Barrier

The following table shows some examples of barriers erected in Hong Kong. Click on the mimic diagrams to see more details :

Project

Characteristics

Mimic Photographs

Vertical Roadside Barrier
for Route 5 - Shatin Approach near Mei Lam Estate

Simplest form of noise screening structure
Effective in protecting low-level sensitive receivers
Can be installed on one side or both sides of carriageway

Cantilevered Barrier
for West Kowloon Expressway - near Lai King

Effective in protecting low to mid-floor sensitive receivers
Can be installed on one side or both sides of carriageway

Central Barrier
for West Kowloon Expressway - near Mei Foo Sun Chuen and Nam Cheong Estate

Vertical barrier installed located in the central reserve of dual carriageway
Effective for protecting low to mid floor sensitive receivers from wide dual carriageways

Noise Enclosure

To function well, a noise barrier must prevent the line-of-sight between the noise source and the receiver. This is not always possible, especially with high-rise noise sensitive uses. In this circumstance, noise enclosures are required to provide appropriate protection against environmental noise for the noise sensitive uses.

In general, an enclosure can reduce noise by more than 20 dB(A).

Similar to noise barriers, noise enclosure should be designed to serve both acoustic and aesthetic purposes.

The following are some common types of noise barriers used in Hong Kong. Please click on the demo button to read the details. Then click on the stop button to stop the sound/demo.

(a) Semi-Enclosure

(b) Full Enclosure

The following table shows some examples of enclosures erected in Hong Kong. Click on the mimic diagrams to see more details :

Project

Characteristics

Mimic Photographs

Semi-enclosure
for Tate's Cairn Tunnel Approach at Choi Hung Estate and Richland Gardens

Effective in protecting high-rise sensitive receiver at one side of the carriageway

Full Enclosure
for Wong Chu Road

Effective in protecting high-rise sensitive receivers located on both sides of carriageway

Architectural Features/Balcony

<Certain architectural features such as fins and balcony can help reduce impact of road traffic noise on residential buildings.

Image of using architectural fins to reduce road traffic noise impact

Image of using balcony to reduce road traffic noise impact

Building Orientation and Innovative Layout

The following illustration explains the idea of using building orientation and innovative layout to reduce the impact of traffic noise :

Image of using innovative layout to reduce road traffic noise impact

In such a design, the building is oriented so that less noise sensitive uses such as kitchen, bathroom and store rooms are located to one side of the flat while noise sensitive uses such as living rooms and bed rooms are located on the other side. The building is so oriented that the side of flat containing less noise sensitive uses is facing the major noise source such as a busy trunk road. This building arrangement can sometimes help to render sensitive development at an otherwise "environmentally unacceptable site" acceptable.

Open-Textured Road Surfacing

There are two main sources of noise from vehicles: the engine and road/tyre interaction.

When traveling on level roads and at high-speed traffic, road/tyre interaction noise dominates. On inclined road or level at low-speed traffic, engine noise becomes dominant.

Most roads are paved with surface that has microscopic grooves which cause the noise to resonate, thereby increasing the noise. But a different material on the road will reduce the noise arising from road/tyre interaction.

Friction course, a special type of bituminous highway surfacing, was originally designed to improve skid resistance by virtue of its open texture. The open-textured bituminous highway surfacing consists of tiny holes making up 20% of the volume and can reduce traffic noise induced by the interaction between road surface and vehicles tyres of high-speed traffic by up to 5dB(A). Please click on the demo button to see the details.

Photo of open texture materials

For information on how road resurfacing using low noise materials helps reduce traffic noise in Hong Kong, please click here.

Acoustic Insulation of Receiver

The provision of window insulation and air-conditioning is the "last resort" in an attempt to abate the residual impact from noise sources not controlled under the NCO, such as aircraft, road traffic and helicopter.

The acoustic insulation will practically deprive the receivers of outdoor activities and an "open-window" life style. While acoustic insulation is commonly found in some western countries, the warm and humid climate in Hong Kong makes it more expensive for noise sensitive uses due to the need to provide air-conditioning for a "closed-window" environment.

The suitable window types for noise insulation are shown in the following table. The table indicates the suitable window type that should be used when the estimated noise level will exceed the relevant standard by ß value.

Table of window types summary

A typical example of this measure is the School Insulation Programme. For details of this programme, please click here.