Continuous Road Traffic Noise Monitoring and Aging of Asphalt Surfaces

A highway in Switzerland has been covered by two different types of asphalt surfaces one after the other and at the same time. Next to each of the two road sections acoustic recording stations were permanently registering traffic noise levels over a time period of two years. In parallel meteorological parameters had been monitored and the road traffic had been counted according to vehicle class by an automatic traffic monitoring station. The sound levels at both recording stations display significant and slightly different increases over the observation period. This indicates differences in aging behavior between the two asphalt coverings. Since the noise level variances due to dependencies on meteorological conditions and traffic distribution are larger than the anticipated changes due to the aging of the surfaces, a stratified sampling strategy has been successfully applied in the statistical analysis of the traffic noise data. Of particular relevance has been the consideration of temperature effects on tyre/road noise. Periodical measurement surveys of sound levels via CPX-trailer and statistical pass-by method and of in situ measurements of acoustically relevant road surface properties show significant temporal changes on both asphalt sections that go along with the results from the permanent noise recording stations.