scope:

Outdoor barriers can serve to protect residents or recreation areas (e.g. parks, gardens, camp sites) from the noise against traffic and industry as well as from noisy recreational facilities.

The use of sound-attenuating barriers will mainly be advisable if

- it is impossible or more expensive to reduce noise at the source.

- their erection is less costly than other noise control measures,

- their effect is mainly required for one direction.

Barriers for the protection against traffic noise are installed as dose as possible to roads and railways. They are used in the form of

- noise barriers,

- artificial earth berms or naturally elevated terrain,

- cuts or troughs,

- combinations of the aforementioned Screening systems,

- lines of buildings or garages.

For the protection against industrial noise the following are preferably used:

- noise screens or earth berms for outdoor facilities working dose to ground level (where the barrier can also conceal the facilities, provided its design is pleasant and matches the environment),

- barriers for sound-radiating openings (a combination with a silencer Is often possible),

- placement of Workshops or Office buildings between the sound source and the Immission point (which also comprises arranging sound-radiating openings on the side turned away from the Immission point),

- flexible barriers in the form of insulating mats which allow enclosing the sound source on more than one side, and which are particularly suitable for use at building sites.

Noisy recreational facilities (e.g. playgrounds, shooting ranges, public open-air swimming pools) allow the use of

- artificial earth berms, or natural or designed elevations in the terrain,

- walls built to fulfil a function or for design purposes, e.g. spectator's stands,

- buildings which are part of the facility

as barriers.

High-rising barriers at the borders of airports, at the transit Strip (taxi way) near the runway and along the take-off runway have not led to a verifiable reduction in sound level [16].

The effect of Screening may become very small because of meteorological influences, where distances of more than approximately 300 m lie between sound source and Im¬ mission point. In such a Situation it should be thoroughly checked whether a barrier is to be applied [16].

Instead of being positioned dose to the sound source, noise barriers can also be instalied as dose as possible to facilities requiring protection. This can be done in the form of

- buildings (which protect their own rear side or further buildings),

- parapets for terraces or balconies,

- borderline walls around estate areas, which serve as sound-attenuating barriers, 

- sound-attenuating earth berms or walls.

Besides noise control, there are other effects of barriers, which may support or prevent their appllcation [2], e.g.

- interception of the line of sight to the sound sources which are regarded as disturbing.

- aesthetically spoiling design and negative effects on the appearance of the town or countryside, 

- blocking of paths (e.g. crossing of roads).