Car transportation process, due to its complexity, can be equated with the normal functioning of the S-K-D system (car-driver-road). Other automotive subsystems, although they define the quality of the car transport process, do not directly affect the flax process, and in a sense they are the background affecting the S-K-D system. These subsystems. will continue to exist, as long as there is an S.D.K., acting as a combination of means for the movement of cargo and passengers.

A system should be understood as a set of all its related components. The system generally creates a specific unity with this environment, in which it occurs, and therefore each tested system is of a higher order, and its components, for my part, they exist as subsystems of a lower order or rank.

During the safety tests of the S-K-D system as a system, its dependence on the environment should be taken into account. whose main element in the case under consideration is society. So. the understood S-K-D system is a social element designed to meet the needs of society in the field of transport of means of production and consumer products. Further consideration of the issue of transport safety may be carried out on the basis of the assessment of the S-K-D system, which appears as a symbiosis of machine and man, sufficiently considering only two couplings, namely:
- participation of the S-D subsystem in the traffic safety management process,

- the process of restoring the safety of the S-K-D system components.

A special criterion for assessing the S-K-D system is the overall time and security of cargo and passenger deliveries, which replaces the general criterion called intact behavior.