AusRAIL, Operations & Maintenance, Research & Development, Track & Civil Construction

Cutting out the noise

noise attenuation

A sustainable solution for when rail and residences meet, STRAILastic have a smarter noise attenuation solution.

Living near a train line has many benefits. Being able to walk to high-frequency services to hubs means less time spent in traffic and easier connections to destinations that are difficult to drive to, such as airports, CBDs, and stadiums. Being within 400 metres of a train station is thought to increase a property’s value by 4.5 per cent, according to research by Luti Consulting and Mecone Planning.

Recognising that the benefits of locating residences close to train station extend beyond individuals to the broader flow of cities, planning authorities have been encouraging increasingly dense residential development within walking distance of transport. In 2017, according to the Australian Bureau of Statistics, around 40 per cent of population growth in Sydney was within 1km of a train or bus station. In Melbourne, the figure is about 30 per cent.

While these figures are undoubtedly good for mode shift to public transport and the liveability of cities, as more people move close to rail lines noise from trains is becoming a greater community concern. Furthermore, as cities trial 24-hour public transport, especially on the weekends, the impact of rail noise is being felt by the community.

Rod Pomroy has seen how these development trends have brought communities closer to rail lines. With an almost 30-year career in the rail industry, Pomroy, now managing director of STRAILastic Australia, has seen the pressures put on rail operators to reduce noise pollution through tighter operator noise licensing from environmental protection authorities around Australasia as high rise residential development expands adjacent to station nodes. Communities have also raised concerns about the visual impacts of large concrete sound barriers along the rail corridors often covered in graffiti.

While the number of people living close to a rail line and subsequent regulations might have increased, what actually causes rail noise has remained constant.

“The majority of noise is from the wheel-rail interface,” said Pomroy. “It’s that wheel squeal where the flange meets the rail head with the rail head roughness.”

To understand the amount of noise that is coming from the train and into the surrounding residences, acoustic sound engineers construct a sound map of the adjacent area which presents the volume levels emitted from the rail corridor. STRAILastic then works closely with the acoustic engineer to determine to best combinations of treatment to show these reductions on the acoustic map.

“A sound map describes visually the impact on adjacent buildings from the noise coming off the railway line, and then describes the stepped change with first the STRAILastic dampers, and then the overlay of the mini sound wall and vertical infill panel. This allows the acoustic engineer to recommend the most effective treatment to reduce noise in the area adjacent to the railway line.”

Developed to meet the needs of railway authorities, the STRAILastic mini sound wall range were designed to fill a gap in the market for an economically and environmentally sound solution.

As a modular system, STRAIlastic is able to combine these products to fit the task at hand.

“You only use these solutions where you need to,” said Pomroy. “First you do the noise assessment, work out where the major impact is and then concentrate the noise attenuation at the particular location.”

For example, on railway embankments above the surrounding area, a simple solution is to install the low profile infill panels which prevent sound from reaching the community below while allowing passengers to look out from the train over the surrounding area. It can be treated aesthetically by attaching a screen-printed scene on an aluminium panel attached to the obverse side of the panel wall. In urban areas where rail lines pass through cuttings or in tunnels underneath homes, the damper would be used in combination with the two ripple wall treatments to cut the noise at the source.

Each product contributes to a noticeable reduction in noise levels, said Pomroy.

“The web dampers reduce noise by about three dBA. Then the mini sound wall or the vertical panel attached to the bridge parapet railings will reduce the noise emitted by approximately another four to five dBA, taking the total reduction to eight dBA.”

Noise through a transom bridge can be significantly reduced by attaching modified STRAIL level crossing panels to seal the area below from the noise on the bridge.

The precise nature of the STRAILastic solution, tailored to the conditions provides cost effective and visually appealing solutions for rail operators rather than existing alternative noise attenuation initiatives of large concrete barriers installed alongside the rail line to cut out noise. The large walls can be a blunt, expensive solution and create a heavy visual barrier in the community which attracts graffiti.

“STRAILastic has another way of doing it and it’s cheaper and more appealing to the local community,” said Pomroy.

What makes STRAILastic more effective is the low profile of their unique design which allows passengers to see from the train. The ripples in the vulcanised rubber surface trap and mix the sound waves effectively cancelling the waves generated.

“When the noise hits that the rippled sound barrier it disturbs the sound waves back on themselves and so it dissipates it”.

Another benefit of the product range is environmental. The panels are made from a vulcanised rubber mineral mix, which is 70 per cent recycled materials, tyres in particular. This avoids the significant carbon cost of concrete.

Designed and manufactured in Germany, STRAILastic rail noise attenuation products have been specifically devised to reduce the airborne wheel rail noise.

Andreas Göschl, business development manager at parent company Kraiburg Strail, said that the products have been developed with specific input from rail operators.

“We have founded a team of specialists who collect direct information from railway authorities in specific countries and through our STRAIL Partner Network, which is active in more than 50 countries, for over 40 years. The team develops solutions based on requirements that come directly from the railway authorities.”

Individual products can also be tailored to fit unique demands.

“For example, we have several versions of STRAILastic mSW that have been adapted to the specific requirement in each country, exactly shaped to the technical envelope,” said Göschl.

Ongoing product development to improve vibration absorption and innovation in new surfaces will continue to improve the product’s capabilities.

With their low profile they do not need any extra planning approvals, unlike larger concrete sound walls. Although mounted near the track, the products have been designed to allow for rail maintenance works.

The mini sound wall, which is located as close to the kinetic envelope as possible, is mounted at the end of the sleeper and the design enables track machine access through the install of gates at regular intervals for machinery.

“Furthermore, we’ve developed a variation of this mini sound wall product where instead of it being on the end of the sleeper, we extend that support further out to allow tamping without removing the panels,” said Pomroy.

Where the products have been installed so far, noise measurement has shown a reduction in noise emitted and local residents have often commented on the difference. In Brisbane, STRAILastic installed the dampers at the entrance to the tunnel which adjoins the northern end of the Merivale Bridge. Residents above the tunnel entrance wrote in after the dampers were installed to say they appreciated the difference.

“In Germany we’ve have similar letters from people living adjacent to the rail lines saying, ‘Thank you I can now sleep at night’,” said Pomroy.

While the systems that STRAILastic has installed in Brisbane and elsewhere reduce the noise impact from existing railways as urban centres densify, new rail projects are required to address both vibration and airborne design within their designs but on some recent projects ineffective noise attenuation has led to post-construction solutions.

“On some recently completed rail projects the designers did a lot of work to try and isolate the noise, but it wasn’t effective enough and additional treatments such as acoustic panels were retrofitted to get the noise to an acceptable level.”

For future projects, noise and vibration options have been significantly improved through continuing research and development efforts with new and modified product range being developed to meet individual project needs. STRAILastic’s in-house design team have recently developed sound-damping panels shaped to the side of tunnels and new combinations of vibration mats and track isolation that reduces the vibration that passes into the surrounding structure.

“I just want people to think about it before they start,” said Pomroy.

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