The LIWAS traffic warning system aims at providing early warning to vehicles about road conditions, such as whether the road is slippery. The LIWAS system is currently being developed and consists of two main parts: sensors for determining the state of the road and a communication infrastructure supporting inter-vehicle communication. This paper presents our results on requirements identification, design, and prototyping of the infrastructure. The infrastructure combines communication via mobile phones with communication based on the principles of ad-hoc networking, and it supports units in being updated during operation. The presented prototypes and associated experimental results demonstrate the main functionalities of the communication infrastructure, and have led to the initial deployment of LIWAS units.