The Mayor's Ambient Noise Strategy - Greater London Authority

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The Mayor’s Ambient Noise Strategy Mayor of London 71 is now quieter tyre-road combinations. Tyre-road noise is typically dominant at speeds above 60 kilometres per hour (40 miles per hour), but is becoming more significant at lower speeds, down to 50 kph (30 mph) or even lower. Tyres on many cars have become wider as they have become heavier. Porous asphalt is especially well-suited to reducing noise on faster roads, especially motorways. Other noise-reducing surfaces may be more suitable for highly urban situations. Some of the new ‘thin’ surfacings may reduce noise even at lower speeds. Stone mastic asphalt (SMA) is a particularly versatile material. Many such surfacings require less planing back and fewer other operations during resurfacing. They use less material and avoid use of some of the noisier construction plant. This is a particular benefit for sensitive times and locations. 4A.25 In deciding whether to use a noise-reducing surface, and which material to specify, changing traffic speed through the day needs to be taken into account. The choice of surface should take account of real vehicle speeds at night, in the evenings, and possibly at weekends, not just in congested weekday conditions. In assessing the noise benefits of different surfaces, account should be taken of changes in sound quality as well as in overall sound energy. Some surfaces reduce some sound frequencies (see Appendix A2 for explanation of acoustic terms) more than others, such that the sound quality becomes less annoying. A surface may give greater reductions when new than after several years of use. The life cycle performance of noise-reducing surfaces needs to be taken into account. Choice of materials for and design of footways, traffic islands and other spaces in addition to the vehicular carriageway needs to have regard to noise. For example, a smoothly-surfaced route should, if possible, be provided for trolleys where early or late loading and unloading takes place in mixed use areas. proposal 6 Transport for London will, and London boroughs and others should, use noise-reducing surfaces, where practicable and cost-effective, and where they do not compromise safety, particularly skidding resistance, and other criteria. This includes: ■ Where possible, prioritising higher speed roads and roads with significant night traffic flows and speeds; and ■ Assessing how the life cycle acoustic performance of noise-reducing surfaces may best be monitored and findings shared. Tree planting, noise barriers, landform and highway structures 4A.26 Reducing noise at source will generally be the first priority, especially in cities. Some form of screening is often seen as the next line of defence - such as noise barriers, mounding or other changes to landform alongside the road. Tree planting needs to be dense, and extend over a belt of
72 Mayor of London The Mayor’s Ambient Noise Strategy perhaps 10 metres to have any real effect. Issues of space and personal safety need to be considered. However, narrower belts of dense vegetation - or even just street tree planting - can subjectively improve people’s perceptions. Trees and other vegetation can make other forms of noise screening more visually acceptable. The amenity, cooling and other benefits to be gained from tree planting reinforce their role. 4A.27 Noise barriers need to be as close as possible to the source, or to the receptor. Roadside barriers need to be continuous over long distances to be effective. Lack of space and frequent junctions make effective barriers impractical on most London roads. Badly-designed barriers can sever communities, attract graffiti, block views, and make people feel less safe. In London, many properties would be too close to the street, or too high, to be effectively screened. However, even if barriers would not reduce noise suffiently at windows of noise sensitive properties, there might still be some benefits for gardens and other open areas. Theoretical performance may not be achieved in urban areas with multiple noise reflections among buildings. There is at present no specific funding for developing noise barriers. Support from adjacent development could be an option. 4A.28 Low barriers can, however, be effective on elevated roads and flyovers. One type of safety parapet which screens noise may not cost more than another which does not. Sound absorbing surfaces on highway structures, such as vertical cutting walls, within tunnel mouths, or on supporting surfaces of elevated structures could reduce noise, and may be more costeffective during refurbishment. 4A.29 In other European countries, more ambitious noise barriers have been installed. Many different materials and imaginative designs have been used. To be effective, urban noise barriers often need to be taller than a typical wooden fence or garden wall. Their length means they become dominant features in the urban landscape. Continental practice demonstrates that successful environments can be achieved where skilled designers make strong urban design statements. By contrast, an apologetic ‘keeping in keeping’ approach can make urban surroundings cumulatively less interesting. Attractive solutions can, however, be expensive, particularly those that involve cantilevering a barrier partially over the road. Combining noise barriers with generation of electricity using photovoltaics (see glossary) may be feasible. 14 Their performance can deteriorate if they are not well-maintained, and they should meet relevant guidance and standards. 15 The screening performance of noise barriers can fall considerably after installation. The quality of the original construction is at least as important as age. Regular checks need to be considered.
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