The constantly increasing participation of cars as means of transport should entail the development of the whole road transport system. The low level of traffic safety on Polish roads results from the insufficient development of road infrastructure, from the more and more increasing traffic flow, from the fact drivers are not adapted to conditions existing in the, sometimes purposely, but often from inexperience or ignorance about the current unfavorable situation on the road. Here, an advanced monitoring of the road transportation system can assure the improvement. The road transport system, as a wide spread object, causes a number of problems concerning diagnosing its state. In this article two examples of relations diagnoser - diagnosed object are presented, the basic one and a more advanced as the second, enlarged by an increased number of signals concerning the state of the object, being analyzed by the diagnoser, received thanks to modern techniques of satellite navigation and active safety systems installed in the vehicle. The moving vehicle has also been used as additional source of diagnostic information.