Aim of this work is to present a metaphor based multilevel interface for an Intelligent Transport System (ITS) designed to handle the transport of hazardous materials. This ITS was developed by the authors in the framework of a research project funded by Apulia Region (Italy). Starting from monitoring some parameters of a vehicle in motion such as position, speed, load balancing, stress conditions, etc., this system identifies various situations such as driver's behavior, hazardous conditions, and so on. In order to represent this information, the authors propose a multi level metaphor based graphic user interface (GUI). The first level of the interface allows for a rapid system view at a glance and is oriented to unskilled users while the second level reports more detailed information for the expert users.