This paper deals with the elaboration of the method of definition of primary and secondary parameters of the rail circuits on the base of the measuring car-laboratory with the help of special program microprocessor apparatuses. It was proposed advanced mathematic model of the information channels (rail circuits) for scientific substantiation of a method of the code parameters measurement. The measurement of current in the rail circuit is carried out in the regime of automatic locomotive signaling. The parameters of the rail circuits are defined by the value of code current of the rail circuits in the beginning and the end of the rail path. The results of modeling are presented for the 50 Hz code rail circuit.