Audio information is the second in importance after visual information. A per- son receives 9 % of information about the world through hearing; however, in the situation of warning about the dangers, audio information has two significant ad- vantages over visual information. First, it causes an immediate response in a person, and secondly, it is perceived from all sides, even if a person does not see the source of the signal. All this applies equally to the audible warning signals of locomotives, which are still sometimes the only way to warn people on the tracks about the ap- proaching train. While the rolling stock of railways underwent significant changes in the twentieth century, which led to a significant increase in speeds and, as a conse- quence, an increase in the braking distances, the sound signaling devices of locomo- tives remained at the level of the 1920s. Large-scale studies to determine the optimal acoustic characteristics of locomotive signals were carried out at Leningrad Insti- tute of Railway Transport Engineers under orders from the Ministry of Railways.