A novel sensor network configuration is introduced for traffic surveillance in Intelligent Transportation Systems. Distributed sensor nodes based on passive acoustic transducers are non intrusively/obtrusively deployed at motorway road-side to provide real-time traffic data collection for dynamic queue/jam detection. The system is capable to provide a complete real-time picture of traffic flow at unprecedented time/space scale. The infrastructure is based on a stand-alone, install-and-forget architecture, featuring an energy efficient protocol for sensor networking and providing connectivity to back-end computing environment via TCP/IP over UMTS. Extensive experimental demonstration is given for long term operation on a motorway test site.