How Acoustic Barriers Work
Road traffic noise reduction from acoustic barriers is achieved through two mechanisms: insertion loss (IL) — the reduction in sound level the barrier achieves compared to the situation without it (measured in dB); and diffraction — sound bending over and around the top of the barrier. A typical solid acoustic barrier 3m high can achieve insertion losses of 8–12 dB. A 6 dB reduction is perceived as approximately halving the loudness. Barriers only protect areas in their acoustic shadow — locations directly behind the barrier and at limited lateral angles.
Key Design Factors
Height
The most important performance variable. Taller barriers provide greater diffraction loss, but with diminishing returns — doubling height from 3m to 6m may only increase insertion loss by 3–4 dB. Beyond about 6m, the visual and practical impact becomes extremely significant and planning approval becomes more difficult.
Length
Barriers must extend sufficiently beyond receptor locations at each end to prevent flanking (sound wrapping around the ends). Rule of thumb: barrier length should extend at least 4–5 times the barrier height beyond the end receptor in each direction.
Mass and Density
For solid barriers, minimum surface mass of 20 kg/m² is required for adequate transmission loss. Gaps at the base and between panels are major performance leaks — a small gap can significantly degrade overall performance.
Absorption
On busy multi-lane roads, sound reflecting from one barrier face can increase noise levels on the opposite side. Absorptive acoustic barriers (with mineral wool or porous concrete facing on the traffic-facing side) reduce reflected sound and are specified where barriers are required on both sides of a road.
Acoustic Barrier Materials Compared
| Material | Typical IL | Durability | Aesthetics | Cost |
|---|---|---|---|---|
| Concrete (solid/hollow) | 10–15 dB | 50+ years | Variable (can be textured) | High |
| Timber (close-boarded) | 8–12 dB | 15–25 years | Natural, popular in residential settings | Medium |
| Steel (profiled) | 8–12 dB | 25–40 years | Industrial; can be powder-coated | Medium-high |
| Recycled plastic | 8–12 dB | 30–50 years | Moderate | Medium |
| Earth bund | 10–15 dB | Permanent | Natural, landscaped | Variable |
| Transparent (acrylic/polycarbonate) | 8–12 dB | 15–20 years (degradation) | Minimal visual intrusion | High |
| Absorptive composite | 12–18 dB | 30–50 years | Functional | High |
UK Standards and Assessment Methods
Road traffic noise is assessed using the CRTN (Calculation of Road Traffic Noise, 1988) methodology within the Design Manual for Roads and Bridges (DMRB), Volume 11, Section 3, Part 7. The Environmental Noise Regulations 2006 require strategic noise mapping around major roads, and action plans managed by local authorities which may include barrier installation programmes. The NPPF requires planning decision-makers to prevent new development from creating unacceptable noise impacts.
Planning Considerations
- Acoustic barriers on the public highway require highway authority approval
- Tall barriers (typically above 2m) require planning permission in most locations
- Visual impact assessment required alongside acoustic performance assessment
- Conservation areas may restrict barrier materials and design
- Landscaping integration — climbing plants, green walls — can improve visual amenity while maintaining acoustic performance
Conclusion
Acoustic barriers are effective tools for reducing road traffic noise when properly designed, built, and maintained. Their performance depends on height, length, material quality, and installation detail. Proper acoustic modelling at design stage is essential. Browse our site safety and perimeter barrier range for relevant products.