Articles
The latest data published by the European Environmental Agency (EEA) coincides appropriately with 2020 being the International Year of Sound. The EEA’s Environmental Noise in Europe report provides detailed insights on noise exposure, impacts on humans and wildlife, and actions being taken to reduce exposure.
In terms of impacts on humans, exposure to noise can result in annoyance, as well as health issues such as stress and sleep disturbance. Across the EU, the EEA estimates that 113m people live in areas of high road traffic noise and 22m people are impacted by railway noise. While the scale of rail noise impact is significantly less than road traffic noise, there is potential for this to increase with more frequent and faster trains. To address this, there have been developments in EU legislation.
The Environmental Noise Directive (END) requires noise maps to be produced every five years for rail, road, airport and industrial noise sources. Last year the third round of maps was published. In association with the maps, rail authorities – in the UK these are the Department for Transport, Office of Rail and Road, and Transport Scotland – are required to investigate locations with the highest noise exposure, leading to the implementation of noise management action plans.
Grinding strategy
A positive side-effect of the change in Network Rail’s grinding strategy to address rolling contact fatigue is a reduction in environmental railway noise. This resulted from lower levels of roughness on the rail head of main lines. Rail roughness and wheel roughness cause wheel-rail rolling noise – the dominant sound source for trains travelling at speeds above 50km/h. Hence this has become a useful UK response to END by demonstrating the benefits of rail grinding and further reductions could be achieved from acoustic-specific grinding.
Additional regulations include noise limits for new rolling stock in the technical specifications for interoperability for both conventional and high-speed trains, and the implementation of track access charging schemes that include noise penalties.
END considers wheel-rail rolling noise and traction noise from moving trains, but railways generate many other sounds. These can vary in volume and character, the latter including frequency content and temporal nature – for example, the intermittent high-pitched squealing noise from rolling stock on tight curves or the continuous low-level hum of a transformer associated with power distribution equipment.
Other sources include: aerodynamic noise from high-speed trains; audible warnings, such as train horns, level crossing and trackside warning systems; and public address systems. While the adverse effects of some of these sources are smaller, their impact on railways’ neighbours can lead to complaints. For many of these sources, the assessment of the impact and the control of the noise are often complex.
Sound demonstrations are increasingly used to review the sounds generated from different designs and to manage the expectations of stakeholders, including the public. These work in a similar way to ‘surround sound’ with headphones or a group of loudspeakers enabling listeners to perceive sound sources at the desired sound level and the desired direction and distance. The demonstrations allow listeners to engage with a simulated soundscape by enabling them to listen as well as critically locate and judge individual sound sources.
Bad vibes
Vibration from railways can also be an issue, particularly for sub-surface tracks where the vibration propagates through the ground into buildings, typically resulting in a low-frequency rumble noise and feelable vibration.
High Speed 2 has kept many acousticians busy as they address the challenge of controlling the noise and vibration from trains travelling at 360km/h for the environmental assessment stage of the parliamentary approval. Future detailed design and the construction process will also test the industry’s expertise and collaboration.
Plenty more work is required as we strive to make life better for those 22m EU citizens who are directly affected by railway noise.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.