Belgium is deploying a large network of traffic cameras and sensors. This nation-wide infrastructure aims at implementing smart city initiatives, better controlling air pollution, responding faster to emergency situations, and increasing security on the roads by better enforcing traffic law. This presentation describes the big data architecture put in place to collect and process in near-real time data generated by thousand of cameras and sensors and how this architecture is implemented using Apache Kafka, and the Play! and Akka Scala frameworks. It discusses the main challenges met during the project and the approaches selected to overcome them and ensure the reliability, scalability, and robustness of the overall infrastructure.