Marek Guzek

With the continuous development of road transport of goods, the issue of safety risks related to the movement of trucks and road trains remains an essential element of the overall road safety system. One of the persistent problems is the braking of such kits, especially in emergencies on the road. The work aims to show how typical changes in operating conditions can affect the basic indicators illustrating the safety of braking (effectiveness indicators, stability symptoms). A simulation method was applied for the analysis, which used a relatively simple (quasi-static) model of the tractor-semitrailer set’s rectilinear motion and models of the braking system and the longitudinal forces in the tyre-road surface contact. Calculations were made for the selected truck-trailer set in nominal condition and for several deviations from the nominal state, such as loading the trailer (load value, location of the semi-trailer’s centre of gravity), reduced surface adhesion, and selected faults of the semitrailer braking system. The results were compared for several qualitative and quantitative criteria for the evaluation of braking safety. Attention was drawn to the problem of the forces in the coupling (which determine the possibility of jack-knifing phenomena), the order of axle locking, and the braking distance. The presented results show that the change of operating conditions as above compared to the nominal condition visibly deteriorates the effectiveness of the braking process. The greatest threat, both related to the braking efficiency and the increase in the force in the coupling, is associated with the lack of braking of the semitrailer axle or a significant reduction in its load. The weight and location of the load’s centre of gravity considerably impact braking safety. In addition to the negative impact on the braking distance or increase in the horizontal force in the coupling, it changes the order of locking the axle. ABS reduces the risk associated with braking safety but does not eliminate it. At the same time, it has been shown that using relatively simple calculation tools makes it possible to indicate the risks related to the braking safety of such articulated vehicles.