The carrying capacity of the railway and the service life of artificial structures primarily depend on the operational category of the structure and the dynamic state: dynamic stability, the condition that dangerous vibrations do not appear, and the dangerous resonance of the amplitude of the oscillations. Studies on the dynamics of railway bridges have gained relevance in connection with the new construction and reconstruction of bridges of high-speed and high-speed railroads. When choosing the restoration measures for the reconstruction of existing railway lines or when designing and building new structures, taking into account the current high operational requirements, a thorough evaluation of the efficiency and reliability of the span structures is necessary, taking into account the type of construction and analysis of the dynamic impact. In the article the analysis of factors is produced influencing on the possible loss of dynamic stability of bars of the latticed truss under act of kinematics indignations of ends of bar at the general vibrations of flight structure caused by dynamic factors accompanying moving of the temporal loading on a bridge. A novelty is made by the account of mutually influencing general and local vibrations of flight structure at the estimation of dynamic stability of the cored latticed truss. The spectrum of parametric vibrations of bars of the latticed truss is investigational in the conditions of remoteness from the areas of dynamic instability. The method of decomposition of decision of differential equalizations of vibrations is applied on the Bessel function with a whole icon. Practical limitation of spectrum of frequencies is got near-by the value of bearing frequency to equal frequency of free vibrations taking into account influence of central forces and also relatively small influence of parametric vibrations in areas remote from living parametric resonance. Taking into account the dynamic stability presented by the authors, it is possible to expand the possibilities of using the existing norms and update them for dynamic calculations of railway metal bridges with lattice trusses, as well as to take into account the main factors that influence the occurrence of additional dynamic influences.