The wireless transmission of sensor data in order to monitor road layer conditions is crucial for the evaluation of road security and traffic networking in terms of V2I communication. In this paper, we present a compact transmission system that operates in the energy-efficient Narrowband Internet of things (NB-IoT) network and can be placed inside the road for communication with a roadside receiver. It features a small and robust form factor, a low cost design and a broad radiation characteristic favourable for additional communication links between multiple road-integrated transmission systems as part of a future V2I network. We present the design, simulations and measurements as a proof-of-concept.