Across Europe, thousands of kilometres of noise barriers are built, upgraded or extended every year. Rising traffic volumes, growing urban areas and stricter environmental requirements are driving continuous investments in noise mitigation infrastructure.
In many cases, existing barriers are simply raised by adding extension elements on top of the wall. From a construction perspective, this approach is straightforward and efficient.
But from an acoustic perspective, an important question arises:
Are we actually improving the performance of the barrier — or are we simply making it higher?
12m-tall noise barriers; the right solution?
In Austria, some motorway sections require extremely high noise barriers to achieve the necessary acoustic performance. One example is the barrier system along the A2 near Wiener Neudorf, where wall heights reach approximately 12 metres. Such cases illustrate how increasing wall height alone can lead to massive structures. This raises the question whether improved edge design could achieve comparable acoustic effects with significantly lower construction height.
Where Noise Barriers Actually Work
The effectiveness of a noise barrier is determined by several key acoustic criteria: insulation, absorption and diffraction.
While insulation and absorption are widely considered in noise barrier design, diffraction at the top edge of the barrier often receives much less attention. One reason may be that only a few products on the market are specifically designed to address this phenomenon.
When sound waves reach the top edge of a barrier, they bend around it and continue to propagate into the protected area behind the wall. This diffraction process determines how much sound energy ultimately reaches the receiver.
In other words:
The acoustic performance of a noise barrier is largely decided at the top edge of the wall.
Surprisingly, however, this part of the barrier often receives the least attention in practical design.
Early Field Validation – ASFINAG Test (Austria)
The acoustic performance of the PIN edge element was already tested in 2008 by ASFINAG, the Austrian motorway authority.
For this purpose, an existing 4-m high noise barrier along the A2 motorway near Laxenburg (south of Vienna) was equipped with the PIN element in order to evaluate its effect under real traffic conditions.
Independent measurements carried out before and after installation confirmed a noise reduction of approximately 4 dB behind the barrier.
The results demonstrated that modifying the diffraction edge of a noise barrier with a combination of geometry and absorptive material can significantly improve acoustic performance — even without increasing the overall wall height.
Current Practice: Height Instead of Edge Engineering
In practice, many barrier extensions are based on relatively simple geometries. Examples include octagonal elements, triangular shapes, curved panels or other variations of geometric extensions.
These systems increase the physical height of the barrier and therefore contribute to improved shielding. However, two important aspects are often overlooked.
First, the geometry of many extensions only marginally influences the diffraction process.
Second, the surfaces of these elements are typically hard and reflective. When sound waves hit these surfaces, a significant part of the acoustic energy is reflected rather than dissipated.
At the most critical point of the barrier — the top edge — this can lead to additional sound energy being redirected into the protected area behind the wall. As a result, the additional acoustic benefit achieved by such extensions may remain relatively modest compared to the structural effort involved.
This raises an important question for planners and acoustic consultants:
Should the top edge of a noise barrier not combine both intelligent geometry and acoustically absorptive materials?
Common Noise Barrier Edge Extensions
Several edge extension concepts are currently used in noise barrier engineering. These include, for example:
• Octagonal edge elements frequently used in Central and Eastern Europe (see image from Poland)
• Delta-shaped elements developed for specific frequency ranges
• Rounded wood-concrete elements
• Various triangular or curved geometries
All these solutions aim to improve the shielding effect by modifying the geometry of the barrier edge.
However, most of these elements rely on hard surfaces and primarily geometric modification, while the combination of edge geometry and absorptive surface materials is less commonly addressed.
Rethinking the Top Edge
Over the past 25 years, CALMA-TEC has been exploring exactly this question.
Instead of simply increasing the height of a noise barrier, the focus was placed on the interaction between geometry and material properties at the point where diffraction occurs. The result of this development is the PIN element.
PIN is not merely an extension piece added to increase wall height. Its geometry is designed to interact with the diffraction process at the barrier edge, while the materials used provide a soft, absorptive surface instead of a hard reflective one.
This combination of edge geometry and acoustic absorption aims to reduce the amount of sound energy that propagates over the barrier.
The objective is simple:
Improve acoustic performance not only through height, but through intelligent edge design and acoustically effective materials.
From Concept to Real Infrastructure Projects
This approach is no longer theoretical.
Several infrastructure projects have already demonstrated the effectiveness of the PIN concept. In these projects, the system was selected specifically to improve the acoustic behaviour at the top edge of existing or new noise barriers.
For CALMA-TEC, these projects represent an important step — not only because of their implementation, but because they reflect a growing awareness that the interaction between geometry and surface properties deserves more attention in acoustic design.
Case Example – Hungary
The PIN concept has also been applied in several projects in Hungary, where acoustic consultants deliberately selected the system to improve the performance of existing noise barriers.
One early application was realised on a motorway bridge along the M5 near Szeged, where the PIN element was installed on top of an existing transparent barrier. Measurements carried out before and after installation confirmed a noise reduction of approximately 3.8 dB.
For the project team, the key advantage was clear: a measurable improvement in acoustic performance without increasing the structural height of the barrier.
Since then several projects have followed in Hungary. (see latest project on Budapest-Belgrade railway 2025)
A Question for the Acoustic Community
Noise barrier technology has evolved significantly over the past decades. Acoustic modelling has become increasingly sophisticated, and environmental standards continue to rise.
Yet one fundamental aspect of barrier design still deserves greater focus:
the engineering of the top edge — both in terms of geometry and surface properties.
If diffraction determines the residual noise behind a barrier, then the geometry and acoustic behaviour of this critical point should play a central role in the design process.
Perhaps the next step in improving noise mitigation infrastructure will not only be building higher barriers — but designing softer and smarter edges.
If you are currently planning the extension or modernisation of noise barriers, we would be happy to discuss new approaches to improving acoustic performance.
No responses yet