The world trend, recently, is the creation of a high-speed cargo rolling stock for speeds with 160 km / h. In these condition, the durability of the structure of the cargo car are relevant. In the process of movement in the design of the car, voltages occur, variables in time. Under the action of alternating voltages in the design elements, the process of gradual accumulation of damage, leading to the formation of microscopic crack, and then to its development and subsequent sudden destruction - metal fatigue. One of the main properties of the wagon is the ability to withstand operational loads acting on it while maintaining this ability without destruction at all stages of the life cycle. The assessment of the bearing capacity is determined by the results of the undercarriage tests, the purpose of which is the definition and assessment of the reserve coefficient of fatigue resistance of the equivalent reduced amplitude of dy-namic stresses. As a rule, dynamic stresses are random due to the perturbing effect on the side of the rail path on the wheeled pairs, which are also random. Therefore, an important section of the study is the choice of methods for obtaining, processing and analyzing experimental data. Improving the reliability of test results is achieved by applying more advanced recording methods and processing results. To estimate the level of loading of the cargo car, methods are used based on the replacement of a real random process by some schematized process, which in terms of the accumulation of fatigue damage should be equivalent to a real process. Of the variety of schematics methods, two methods are distinguished - the method of complete cycles and the rain method, which most fully reflect the real process. The advantage of the "rain" method is the ability to process the process in real time. However, the algorithm of the "rain" method is quite complicated and does not allow processing large amounts of information. In this regard, the method of maximum discharges was proposed, which is a type of full cycles method and allows you to process an unlimited amount of information online. The schematic process is divided into classes - voltage amplitudes values. Depending on the distribution of voltage amplitudes in classes, the frequency (probability) of amplitude in the class is established. The reduced amplitude of the dynamic voltage is defined as the amount of products of the likelihood of entering each class on the average magnitude of the voltage amplitude in the class. Key words: cargo car, process, dynamic, voltage, amplitude.