Noise mapping points the route to an ambient noise strategy
Noise mapping is a major tool in the Government's development of a strategy to tackle ambient noise. Philip Evans, Operations Director and John Rowland, Acoustic Consultant, of RPS Planning, Transport & Environment at Tonbridge, give an overview of this technique and outline what's in store on this front
Environmental noise pollution
To many, the complex nature of mapping environmental noise pollution, the associated transmission paths and people's rather subjective perception of what constitutes loss of amenity or a person's quality of life, seems an impossible task. However, noise is rather specific, in that it tends to be a more localised issue, unlike air quality, which tends to be trans-boundary. Furthermore, localised factors, such as highly built-up areas causing reflections and canyon effects, and soft ground, can significantly affect noise levels at receptor locations.
Many procedures have been formulated to calculate levels of noise from a number of sources, the majority of which relate to transportation modes, notably roads (Calculation of Road Traffic Noise (CRTN), 1988) and railways (Calculation of Rail Noise (CRN), 1995). Environmental noise, in most instances, consists of noise from a wide number of sources near and far, which, until recently, tended to be assessed independently.
Both CRTN and CRN originated from the necessity to determine entitlement under the Noise Insulation Regulations for road traffic noise and noise generated by railways, respectively. Both provide guidance on the calculation of noise for each source. Noise mapping leads some way in bringing together the formulated procedures for each separate noise source, to give the overall noise "picture" at a particular location, although there is still need for further research and agreement on the methodologies to be adopted universally throughout Europe.
A European Union initiative, (Directive on the Assessment and Management of Environmental Noise) soon to become law, it is envisaged, requests that all member states carry out environmental noise mapping. The emphasis for environmental noise to be given the same priority status as other forms of pollution has come about by the increasing numbers of inhabitants being exposed to noise at levels detrimental to health or likely to give rise to annoyance, resulting from increased road, railway and aircraft traffic generated noise, and an increasing proportion of the population living in close proximity to these noise sources.
Noise mapping is considered to be a quantitative data gathering exercise and will, ultimately, be used to develop future noise policies/strategies to improve peoples' quality of life. It is understood that as part of the Government's commitment to the task of noise mapping, £13 million has been allocated for the exercise. DEFRA has appointed Schal International Management Limited to project manage and appoint the specialist sub-contractors required, to carry out the noise mapping of England.
It is understood that England will be broken down into thirty zones of varying size, with each zone equating to a contract package, with Schal appointing the first five zones to noise mapping specialists from July 2002. It is envisaged that the noise mapping work will be completed by April 2004. A timetable for the exercise of noise mapping has been planned which will see maps being produced for:
- all urban areas with more than 250,000 inhabitants and those areas close to major roads, railways and airports, by 2004; and
- all urban areas with more than 100,00 inhabitants by 2009.
The year following the production of each of the above noise maps, action plans will be formulated to reduce noise levels but the degree of reduction has yet to be agreed. It is proposed that the action plans will be updated on a five- yearly cycle and be incorporated within the National Ambient Noise Strategy - NANS.
The DEFRA funded mapping programme necessitates that contractors use commercially available computer based models to calculate the emission levels from roads, railways, ports and industry. An altered version of the CRTN procedure is to be used in the computer based models for calculating road traffic noise so as to obtain LAeq levels rather than LA10 levels. Other procedures to be adopted within the computer based models include CRN for railway noise and other sources using methodologies in ISO 9613.
High-speed rail example
Many organisations have had much experience in using CRTN and CRN methodologies. RPS is one such organisation, having had experience in the modelling and assessment of over 100km of high-speed rail including the development of assessment methodology and prediction modelling, much of which was incorporated into CRN.
The principal problems, having been highlighted by other European members' experience in noise mapping, is the compatibility and interaction of all the input data necessary to run the computer based models. Extensive digital data information is required and it is this that has caused some uncertainties. The availability of data and data from different sources has caused problems, along with the potential compatibility of the software tools used.
Many commercially available noise mapping programs exist (W S Atkins' NoiseMap 2000, Cadna A, LIMA and Sound Plan) and all promise to be the ideal tool. The common factor with all such systems is the combination of noise propagation calculations with a mapping and scheme editing facility, consisting of geo-referenced, three-dimensional input data, usually associated with Geographical Information Systems (GIS). GIS have been primarily used as a planning and management tool for all geo-referenced data. The interaction of the calculated acoustic parameters in association with GIS mapping systems results in a noise map.
Another primary objective of the mapping exercise is for the consultants engaged
in the mapping to liase and develop working relations with local authorities,
and offer interactive training, where requested. Through this, it is envisaged
and anticipated that full co-operation and assistance will be provided by those
local authorities having considerable knowledge of the source data required
for the exercise, thus greatly assisting the fundamental data gathering process
- a significant factor in the noise mapping exercise.