In order to have a good understanding of the environmental acoustic effects of traffic it is important to perform long term monitoring within large areas. With traditional monitoring approaches this is quite unfeasible and the costs are relatively high. Within TNO a new wireless monitoring approach has been developed which is based on low cost acoustic sensor nodes. These sensor nodes were recently developed and primarily consist of a standard sound level meter which is coupled to a wireless sensor platform. Based on these sensor nodes a wireless acoustic sensor network can be set up, which makes it possible to monitor a large area during several weeks at relatively low cost. The network is self organizing and data is sent to a central unit via multihopping. Results of a field test in an urban area where a wireless network has run for several weeks will be shown. Also a comparison of the measured results with output of a traditional acoustic model will be made.