The algorithm of constructing the confidence interval of the model estimating the reliability of liner-tamping-straightening machines. The basis for assessing the reliability of transport-technological process initiated the concept of reliability, as the probability of reaching a liner-tamping-straightening machines ultimate goal in the manufacture of track work. One of the main factors reliability of track machines is the utilization of their time and availability to work. The guidelines are outdated factor data used during the working time that must be updated, as the machines are constantly being improved. According to the results of field testing of the liner-tamping-straightening machines was established database of values of the coefficients of availability and utilization over time. The data base values were recorded, the last two stages of verification: logical and mathematical. In the article the example of constructing a confidence interval values of the coefficient of use of time depending on the complex index of reliability: availability. To create the model formed the sample values from the database. After sampling in accordance with GOST R 8.736-2011 State system for ensuring the uniformity of measurements. The direct measurement repeated. Methods of processing the results of measurements were tested for their adherence to the law of normal distribution using the goodness of fit Pearson. Then built a model of the utilization of time depending on the availability liner-tamping-straightening machines (regression equation) and the confidence interval of the model. The proposed model works liner-tamping-straightening machines allow us to predict the main complex organizational and technological performance of a specific machine at the design stage of technological processes of track work. This method is versatile and can be used to assess the technical reliability of any machine systems, complete sets and individual cars.