The need to increase the speed of movement and monitor the technical condition of the railway plan leads to the need to study the effect of the state and the parameters of the curves on the smoothness and safety of train traffic. The technique used in the work provides for the analysis and evaluation of initial data on the state and parameters of the curves that are used in track distances. The results of the analysis of the survey of the curves at the Sinelnikovo-Chaplino section for the time from 2013 to 2016 are presented in the article. It is shown that the final result brings subjectivity, qualification of the performer and other factors. As a result of the straightening operations performed by the VPR machines, the curve does not correspond to the initial passport data. The technique proposed by the authors makes it possible to estimate the intensity of the build-up of residual deformations, their influence on the smoothness and safety of train traffic. When designing road repairs, it is possible to achieve a significant gain in time by resuming the design radii, establishing a path to the design position with in-line maintenance and repair robots by machines. Scientific approaches to assess the state and parameters of the curves in the plan and their impact on the smoothness and safety of train traffic have been developed. The system of criteria for assessing the state of curves is supplemented, which affects the accumulation of pathway disorders in the plan, calculation formulas are proposed for determining the permissible speed if the taps of curvature and the elevation of the outer rail do not match in the curves. The results obtained will be useful for carrying out measures to increase the speed, smoothness of traffic, ensure the safety of train traffic in curved sections of the track, especially in the directions of high-speed train traffic.