Road traffic accidents, especially occurring on road sections outside of populated areas, are characterized by high severity of consequences and, therefore, are one of the main safety problems of the technosphere. Studies of many authors confirm the importance of the influence of meteorological parameters on the accident rate. However, most results don’t contain quantitative data demonstrating how risk of occurring a car accident depends on weather conditions. Research of this article assesses the impact of five main meteorological parameters on the accident rate using as example one of the Russian Federal roads. Nonlinear dependences of weather conditions and road accident risk were obtained by means of calculation of frequencies. The results are presented in the form of graphical dependencies. As a result of approximation there were found formulas that describe the relationship between values of meteorological parameters and the variation of a car accident risk. According to probability theory, the mathematical model can be based on the multiplication of risks caused by each meteorological parameter.