Measuring Road Traffic Noise

As part of an overall measurement programme to monitor road traffic noise in Århus (Denmarks second largest city), the Local Authority set up a noise measurement station on one of the major approach roads to Århus Harbour. This noise measurement station continually measures noise levels and can give a round-the-clock picture of noise level variations.

Like most other districts, Århus Local Authority had used simulation models to determine noise levels, and only made limited use of the actual measurements. But in a new move, and as part of a comprehensive measurement programme to monitor traffic in the environment, they invested in a noise measurement station (a Brüel & Kjær Noise Monitoring Terminal with GSM modem and Noise Monitoring Software), and placed it on one of the major approach roads to Århus Harbour.

In addition to the noise measurement station, the monitoring programme comprises a comprehensive noise survey of the noise levels on all building facades in the district, random estimates of noise levels, and measurements and estimates of air pollution and traffic volume.

The Measurement Station

The noise measurement station was set up in conjunction with Brüel & Kjær and was designed to continually measure noise levels and store the information in a database. The results are measured per hour and per 24 hours in accordance with the new Environmental Noise Directive 2002/49/EC of 25 June 2002 on assessing and controlling external noise in the daytime, evenings, and at night .

The measurement station has been constructed so that it can be moved around, and is equipped with a modem rather than a fixed network connection. The station is connected via GSM modem to a static PC, which automatically dials the measurement station once a day to gather measurement data and store it in a database. It is also possible to make ad hoc calls to the station, thus opening an online connection to monitor the situation at the measurement site in real-time.

Positioning of the Measurement Station

The choice of location is based on ever-increasing traffic volumes, the broad traffic composition, and a particular concentration of residences in the immediate vicinity.

The measurement station is placed 4m above the ground on one of the approach roads to Århus Harbour. The width of the road is about 35m, divided into a cycle path and footpath on both sides, plus four vehicle lanes and approximately 5.5m of grassed and treed central reservation. Approximately 16,500 vehicles a day drive along this stretch, 15% of which are heavy vehicles. The speed limit is 60km/h. A comprehensive survey of noise throughout the district using calculation software estimated the noise level to be 70dB(A) 10m from the middle of the road, and 72dB(A) at the measurement point.

Why Carry Out Noise Measurements?

The aims of supplementing noise estimates with a permanent noise measurement include gaining a picture of how the noise levels vary over the day, and enabling a comparison of measurement data with estimated results.

A comparison of measured and estimated results will be used for general planning, to convey the concept of noise, and to increase the reliability of the estimates, since these are often questioned. This can be due to the difficulties of relating to a noise level expressed as a daily average, when in fact there are periods with higher and lower noise levels than the average.

Measurement Data

The measurement data for December 2002 and January 2003 shows that, in general, the noise levels measured at the measurement station were high. Fireworks around New Year contributed greatly to these high levels. However, the noise monitoring software can remove these events from the overall levels to allow comparison with the result from the road noise model. By comparing the measured and estimated values, it can be seen that the estimated values are generally higher than the measured ones. It is seldom that values higher than the estimated daily base value are recorded for the period in question. It was, generally, a very dry period, but in damp periods, values above the estimated ones are expected.

The Future

Measuring traffic noise is still relatively new to Århus Local Authority who, at the time of writing, only have three months of measurement data. The full benefits of the data will not be known until a full year of measurement results are available only then will it be possible to see how noise levels vary annually as well as daily.

There are plans to extend the noise measurement with the addition of permanent traffic counting to classify the vehicles, so that measured noise levels can be compared with information on traffic volume and composition. It is also possible to compare the results with meteorological data from an air measurement station that is also part of the Local Authoritys environmental traffic survey.

Other future plans include publicising the measurement data, so that local residents can be kept informed of the noise situation, and gain a greater understanding of the concept of noise. This will become easier when the correlation between measured noise levels and actual traffic volumes at a known locality can be shown.

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