Engineering

Engineering requirements that should be considered when designing noise barriers are summarised below:

• Design Life;
• Wind loading including the effects of dynamic loading due to passing vehicles;
• Seismic loading;
• Snow loading (if any) on the barriers;
• Self weight - the dry weight to allow an estimate of sound insulation to be made and, where appropriate, the wet weight;
• Constructability - the ability to build the structure when considering all of the site constraints;
• Impact loading, including impact of vehicles and impact of stones and other debris during normal road use;
• Bund slopes and type of material being used for construction;
• Interruption of overland water flow paths; and
• Clearzone distances, as well as allowances for street furniture e.g. signs and gantrys.

Safety

Noise barriers should be located beyond clearzones or protected by road safety barriers that comply with NZTA standards. Where circumstances permit, modified concrete safety barriers can address both road safety and noise issues as a single cost-effective solution. Additional safety issues to consider include:

• Light reflection glare from some noise barriers e.g. metal, glass, acrylic;
• Impact of stones during normal road use;
• Secondary safety associated with risk of falling debris after impact (this is particularly important when barriers are installed on bridges or between carriageways);
• Provision of access and egress for people and vehicles in an emergency and for maintenance;
• Where there is a risk of vehicle impact, transparent panels should be made shatterproof by using laminated glass or embedding fibreglass within acrylic sheets;
• Avoiding permanent shadow zones which encourage ice formation on the road;
• Wind gusts generated by noise barriers may travel across nearby traffic lanes and upset the stability of vehicles and surprise drivers. High sided vehicles and motor cyclists are especially at risk; and
• Flammability and fire risk.

Crime Prevention through Environmental Design (CPTED) provides a framework for incorporating crime prevention through quality urban design, and should be considered in noise barrier design. Applying CPTED principles such as passive surveillance or creating a sense of community ownership can reduce the motivation to offend. In regards to noise barriers, the risk of crime can relate directly to the noise barriers such as providing access to structures for graffiti, or indirectly, by creating an unsafe environment for the public.

Environmental

The construction of a noise barrier may influence a range of environmental issues besides just noise. During the planning and specification process of designing noise barriers consideration should be given to sustainability issues. The possibility of birds flying into transparent noise barriers is a design consideration.  The impacts of air pollution in regard to noise barriers is an emerging yet potentially significant consideration when it comes to assessing how noise barriers may affect human health.

Maintenance

In summary, maintenance considerations include:

• Materials - material selection for noise barriers has important implications in reducing the need for ongoing maintenance as well as considering what is appropriate to the surrounding landscape of an area, as well as the preferences of residents.
• Construction - the use of smaller sections of replaceable panels within a noise barrier can provide a faster and more cost effective maintenance solution when barrier sections require replacement or repair.
• Access - doors (or gaps between overlapping barriers) may be required to give access for maintenance or emergency along with pedestrians, cyclists and residents.
• Boundaries - boundaries and placement of fences are an important consideration for the repair and maintenance of the barrier and vegetation from within the NZTA land.
• Cleaning - cleaning requirements from contaminants such as water splash and airborne grime should be considered in the design of noise barrier surfaces.
• Vegetation - plant species selection for use in conjunction with a noise barrier should be fast growing, self seeding, hardy species of at least a 20 year life span, which require a low level of maintenance.
• Graffiti - graffiti mitigation measures should be based upon the CPTED principles of: surveillance (e.g. lighting where appropriate), access management (e.g. restricting access through physical barriers), territorial reinforcement (e.g. community art), and quality environments (e.g. easy graffiti removal).

Material selection

A detailed summary of general design advantages and disadvantages for common noise barrier panels/surfaces is given within the Noise Barrier Design Guide - concrete, timber, transparent panels, metal, earth bunds and absorptive surfaces.