GIS tool for management of traffic noise in Geneva
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The instrument described herein is the result of the integration of a set of specific tools necessary in the legal decision process for traffic noise abatement. It consists of five independent modules and uses the vast set of layers of information, made available to members of the SITG (Système d'Information du Territoire Genevois : information system for the Geneva territory). Its development began in 1993 inside the SPBR, the cantonal service specialised in the protection against noise, and is since, in constant improvement taking advantage in the technological advances including the new data bases, new computation models and decision-making tools. When using the traffic noise management system, the first module must identify the roads, which needs to be improved in terms of noise pollution. It is just a relatively crude model of sound emission based upon the road network map and elementary data about traffic (speed and composition). This step results in traffic road maps where the regions above the legal limits for ingoing noise are clearly shown. The next module will generate the “survey of traffic noise map” starting from intensive measurements made on the spot and trough a 3D acoustic modelling whose purpose is to interpolate and smooth the sampled data. The availability of the “survey” of 39000 building façades on the Internet since 1999 is the final result of this stage. The “survey” contains for each façade, the mean day and night noise exposure along with the building affectation, every stage classified following the criterion specific of the Swiss legislation : sensitive or not sensitive to environmental noise. Recent developments have been added to the user interface in order to facilitate its updating with data regularly recorded in the field. The next module : constructing priority lists for improvement works by applying the multi-criteria decision-making tool Electre III to the ingoing noise “survey” and data related to population and building usage - allocation. The way priority is defined depends upon the level of ingoing noise level, the number of people affected and the possible presence of highly sensitive buildings (such as schools, hospitals or socio-medical establishments). The resulting lists are periodically published in the form of a pluriannual plan (10 years). The noise prediction and assessment module computes the expected future ingoing noise (immission levels) using the external acoustic computation model (IMI 5). To this effect, it uses data including local topography (surface model), the road network map, the building locations and traffic density and composition. The adequacy of various improvement scenarios is judged by the amount of reduction in ingoing noise emission and immission with respect to the initial state. The simulation results are presented under the same format as the “survey of traffic noise map”, allowing for a direct evaluation of the efficiency of the proposed solution. Then, the last module helps to define the efficacy and efficiency of each scenario in order to evaluate the cost/usefulness ratio using predefined comparison criteria. This will help to finally decide to implement or not, or re-optimise a particular improvement project. The input data for this module consists of the built area for dwellings and activities, the mean construction costs, the improvement costs, of acoustic insulation and their repay rates as well as the fraction of cured buildings once the improvement is done. The tool for traffic noise management whose structure and working are exposed herein has already been used in the context of the “Plan des mesures d'assainissement du bruit routier” (Plan for traffic noise abatement). Five projects for improvement of cantonal highways and the freeway are under way or partially implemented. At this moment, four teams of engineers and architects are working on approximately twenty technical projects which should answer the preoccupation of most of the population : a significant reduction in noise nuisances and improvement of the perceived life quality in the city.