Although the acoustics function is the primary reason for building a noise barrier, this should not be done in isolation or to the detriment of the surrounding landscape and its visual context.

The following principles should guide the location and design of noise walls:

Integration

Noise walls should integrate with the design of the overall road corridor and complement the road structures, landscape, roadscape and any public art elements of the project. A long term strategy for the design of the entire corridor should be formulated early on, especially if noise walls may be added later.

Proximity

Noise walls should avoid over-shadowing properties and blocking sight lines for surveillance purposes. A balance needs to be struck between reducing traffic noise from the road and potential impacts on personal security.

Location

In suburban or rural environments, landscaped noise mounds can offer a more attractive solution than noise walls. Mounds can be used on their own or with a low noise wall on top. They also provide and opportunity to utilise excess fill from a project and to locate and integrate pedestrian and cycleways into a project.

Safety

It is inappropriate to design the road face of a wall with detail that could distract a driver. However, over-simplification and monotony should also be avoided. A system of simple, abstract, linear patterns can be very effective.

Height

Consider limiting the height of the noise wall to balance noise and visual impacts. Separating and overlapping walls can accommodate any necessary changes in height, horizontal alignment, form and material. Angles and sharp changes in direction should be avoided.

Verticality

A slight lean outwards can bring a considerable improvement in the visual impact of the wall on road users, reducing the ‘tunnel’ effect. Care needs to be taken to avoid reducing the ‘effective’ height of the wall and reducing its acoustic performance.

Views

Noise walls should avoid blocking significant views of the surrounding area both towards and from the road. In special circumstances transparent walls can be used to open up views to landmarks and special vistas. Competing demands to maintain views and provide appropriate noise mitigation need to be balanced.

Form

Consider noise walls as three-dimensional pieces of design with two faces performing different functions. The inner-face is viewed at speed by road users. Their perception is fleeting and only bold designs, geometric patterns and the overall shape of the wall will be viewed. The outer face is viewed from the landscape or surrounding urban area. The noise wall will form a static, permanent feature in the environment and depending on the proximity of viewers, construction and design details may be visible.

Materials

When selecting materials, consideration should be given to their acoustic performance, durability, weathering, ease of maintenance, vandal and graffiti resistance. Noise walls should be designed to retain their noise attenuation performance for a minimum of 20 years.

Detailing

If a noise wall will be viewed from an adjacent residence or pedestrian route, it requires quality detailing and an attractive composition of wall and landscape. Consider tapering the ends of walls into adjacent landforms.

Consistency

Noise walls should be consistent (in materials, general form, colour and detailing) along the length of a road corridor. Avoid frequent changes in design or stepping of the top of the wall as these may be distracting for road users and visually have a jarring effect. If steps are required, ensure they are small and regular.

Landscaping

Planting can be used to complement or screen a noise wall. Planting is especially important on the outer-face of the noise wall where it can help integrate the wall with the wider landscape or provide an attractive interface with nearby properties, public spaces, footpaths and cycleways. Tall planting behind the wall can break down the dominant effect of the top of the wall. Landscape designs must allow for access to the wall for maintenance. Ensure there is sufficient space for plant growth and soil nutrition.

Surfaces

If artworks are to included these should be integral to the design of the noise walls and not be regarded as an applied finish to a wall designed purely on engineering grounds. Surface finishes are very important for amenity and maintenance reasons. They include a combination of colours, textures and patterns.

Length

Excessively long sections of noise wall on both sides of the road should be avoided.

Alignment

Generally the wall should follow the geometry of the road surface. The top edge of the wall is one of the strongest visual elements and requires careful consideration. Horizontal alignment with the carriageway is also important, however curved walls can help to create a sense of place and manage changes in alignment. Care needs to be taken to ensure effective acoustic performance of the wall is maintained.