Having a good understanding of the environmental acoustic effects of traffic in urban areas is important but still a difficult task. Long term monitoring within large areas is needed to provide actual data for taking appropriate and cost efficient measures; to asses the effect of measures by comparing before and after implementation and to have an instrument for policy making. With traditional monitoring approaches this is quite unfeasible and the costs are relatively high. Therefore a new wireless monitoring approach has been developed which is based on low cost acoustic nodes. With these nodes a wireless acoustic sensor network is set up, which makes it possible to monitor large areas during several weeks at relatively low cost. The network is self organizing and the data is sent to a central unit via multi-hopping. Results of field tests in urban areas will be shown together with comparisons of the measured data with predictions of traditional acoustic models. Finally, a model based approach to couple the measurements with efficient acoustic models to create dynamic noise maps and preliminary research results of retrieving additional information from the measurements will be discussed.