Improved GIS-based Methods for Traffic Noise Impact Assessment
NIELSEN O A, Technical University of Denmark and BLOCH K S, TetraPlan Ltd. Consultants, Denmark
When vector-based GIS packages are used for traffic noise impact assessments, the buffer zone technique is usually employed for the study so that: 1. Buffer zones repre- senting different noise levels are generated for each road segment, 2. The buffer zon
When vector-based GIS packages are used for traffic noise impact assessments, the buffer zone technique is usually employed for the study so that: 1. Buffer zones repre- senting different noise levels are generated for each road segment, 2. The buffer zones for all road segments are smoothed together, and 3. The numbers of buildings within the buffer zones are enumerated. This technique provides an inaccurate assessment of the noise propagation, since it does not correct for the barrier and reflection effects caused by buildings. However, the use of more advanced methods on a large scale has been unrealistic due to the amount of data as well as the complexity of the calcula- tions.
The paper presents the results from a research project, where the traditional noise buffer technique was compared with a new method, which includes the above men- tioned corrections (TetraPlan, 1996). Both methods follow the Nordic Noise Model; though the traditional buffer technique ignores parts of the model. The basis for the work, was a digital map of roads and building polygons, combined with a traffic and road database and the Danish Building and Residence Register (BBR). The new method accounts for the barrier effect of buildings. To improve the results, a 3-D model was 'synthetically' created from the 2-D digital map by utilising the information in the BBR register. Thus, the method can also estimate the noise on each floor and it accounts for the differences in the barrier effect between tall and low buildings.
In order to test the methods, total noise impact assessments were made for the munici- pality of Middelfart (20,000 inhabitants). The practical testing of the methods showed that the traditional noise buffer technique compared with the new method systemati- cally overestimated noise-affected residences by 17% and overestimated strongly- affected residences by 282%. Thus, the traditional buffer technique provides unreli- able results in urban areas compared to the more detailed method.
Association for European Transport