Can we put a lid on motorway noise?

The major motorways in, among other places, the capital region are the cause of significant noise impact on the residential areas located alongside them. There are several examples where both affected residents and, increasingly, politicians wish for action to solve the noise problems.

Traffic noise can limit urban development

Residents desire better living conditions with less noise both in their homes and in outdoor areas. The noise zones around motorways mean it can be difficult to find new available spaces for urban development that are not already impacted by noise levels above the Environmental Protection Agency’s recommended thresholds. This limits the development opportunities for several municipalities.

Solutions to the noise problems

Many solutions are continually debated in public and technical forums. These include:

• General reduction of speed on stretches of road near dense residential areas,
• Speed reduction during nighttime hours,
• Limiting heavy traffic, e.g., at night,
• Use of noise-reducing road surfaces such as porous asphalt,
• Introduction of quieter tires,
• Installation of noise-dampening crash barriers,
• Establishment of new, and the raising of existing, noise barriers and earth berms,
• Use of local noise barriers to shield primary outdoor areas at dwellings,
• Creation of “quiet” oases in noise-impacted urban areas,
• Use of noise-insulated window and facade solutions, and
• Covering (tunnelling) of roadways.

Covering motorways as a possible solution to noise problems

In recent years, in the capital municipalities—and perhaps especially in the Copenhagen western suburbs—focus has been directed toward a possibility previously overlooked or quickly dismissed: whether it is feasible to fully cover motorways, or at least those stretches that cause the greatest noise exposure locally.

The immediate objection has often been that such covering is both technically very challenging and economically unrealistic. To provide a more qualified debate, this article presents several international examples where complete or partial covering has been used to reduce road noise. At the same time, the covering has enabled new uses for the areas that are no longer noise-impacted.

The Motorway through Tårnby

The first example is Danish and originates from Tårnby [1]. In connection with the construction of the Øresund Bridge to Sweden more than 25 years ago, a new motorway stretch cut through some residential areas in Tårnby Municipality. Along one section, the motorway passed close to four seven-storey residential blocks which would have been exposed to high noise levels.

The solution was to cover around 700 meters of the motorway with a concrete deck. This resulted in a significant reduction in noise for the residential blocks. Furthermore, green recreational spaces were established on top of the concrete deck, so the motorway did not split the urban area in two. Instead, the neighbourhood was unified around the green areas. The project was financed as part of the overall Øresund fixed link infrastructure scheme.

Motorway A7 in Hamburg

Motorway A7, which carries traffic north out of Hamburg, has for many years had three lanes in each direction. Parts of the road pass close to residential areas that are heavily impacted by noise [2]. There are also a number of undeveloped areas next to the road, which cannot be built on due to noise. Work is now underway to expand the road with yet another lane in each direction. Noise reduction is a prioritised part of this project.

An essential part of the expansion is the decision to cover a total of 3.6 km of motorway with a concrete deck. This removes most of the traffic noise on these stretches. The solution offers several benefits:

• Many existing homes receive a substantial reduction in noise,
• New, "quiet" green areas are created,
• The two urban areas on either side of the motorway are linked by new green spaces and pathways built above the covered sections,
• Areas previously impossible to build on due to noise can now be used for new housing and more. The sale of building plots can help finance the covering.

The Melbourne Noise Tube

Outside Melbourne in Australia, a brand new six-lane motorway was planned. Part of it was built on a bridge over existing roads and large green areas. Along one stretch, the motorway passes very close to a 19-storey residential block, which would have been exposed to high noise levels if significant noise protection had not been established. Authorities required noise shielding.

The private company responsible for constructing and operating this toll motorway decided to cover it with a light structure with partially transparent elements. This solution offers several advantages:

• The residential block receives effective noise protection,
• Large open areas along the motorway get considerable noise reduction and can continue to be used as attractive recreational spaces for both residents and the neighbourhood.

Pilot project using solar panels for covering

In Germany and Austria, there is an ongoing pilot project where solar panels are installed as a roof over motorways [3]. The aim of this covering is to reduce surrounding noise. Simultaneously, electricity is produced and can be sold. The earnings can be used as part of the project’s financing, e.g., as loan repayment for the project’s realisation.

Currently, some areas in Denmark are used for installing electricity-producing solar panels. This is often an aesthetic challenge and takes up land that could be used for agriculture or recreation. If solar panels could instead be integrated into road coverings, land would be freed up for other purposes.

Transparent covering in Poland

Motorway S8 in Warsaw passes very close to the Bródno urban area, which has many residential blocks. To achieve significant noise reduction, a 1,200-metre stretch of the motorway was covered [4]. The cover is a lightweight steel structure with transparent glass panels. The glass panels are not installed in the middle of the road, allowing for ventilation and fresh air to enter the covered section. Emergency doors have been established, creating escape routes at every 200 meters along each side of the road.

Benefits of covering

• Significant or total noise reduction,
• Two city districts can be linked together by recreational areas and pathways instead of being separated by the motorway,
• New areas for sports facilities and recreational spaces,
• Construction of new housing etc. on top of covered areas,
• Enabling construction on areas adjacent to motorways previously too noisy to be built on, and
• Integration of electricity-producing solar panels as part of the covering.

Conclusion

It is not unusual in urban planning to have considered covering motorways and separating the noisiest traffic from pedestrians, other vulnerable road users, housing, and businesses. In planning and establishing the Paris district La Défense in the 1950s and 60s, through traffic was carefully routed to minimise nuisance to the new area. Boulevard Périphérique, Paris’s heavily trafficked ring motorway, is covered along many sections to reduce noise [1]. In some sections, a light cover has been used, which is not suitable for walking or building on. In other areas, a concrete deck has been built with recreational spaces and football fields. Some plans envision covering with high-rise buildings above; here, the sale of building plots could totally or partly finance the cover.

Covering a motorway is a visually significant measure that will greatly affect the urban environment. It is therefore important to involve expertise within urban and landscape architecture during the planning process.

Along, for example, the Køge Bay and Hillerød motorways, there are stretches with up to 100-meter-wide areas on both sides of the road to ensure distance to noise-sensitive residential buildings. If the motorway noise were "capped," these large areas could be used for urban development. The sale of these areas, as part of this, could help finance a covering.

In future projects, it could be considered to use electricity-producing transparent solar panels instead of ordinary glass. Income from electricity sales could partially repay the investment in covering.

Today, motorway noise has received more attention as a negative effect that bothers many and even makes some seriously ill. There is therefore a basis (with evidence for some illnesses) for adopting a more holistic approach in motorway planning, and socioeconomic aspects of motorway impact should be weighted higher than before. Thus, even more costly solutions could become part of the fight against noise.

References

1.Støjafskærmning - et idékatalog. Vejdatalaboratoriet, Vejdirekoratet, rapport 81, 1989

2.Livinggroofs, 2022. Hamburg to bury the A7 motorway – as Linz did over seven years ago

3.fraunhofer, 2023. PV-Süd – PV Roofing Over Roads

4.koenigstahl, 2014. Acoustic tunnels Warsaw