Statistical analysis of railway curve squeal occurrence on the low and high rails in relation to environmental conditions

Abstract Railway curve squeal is a significant source of environmental noise, arising from friction-induced instabilities in the wheel–rail contact. These instabilities are influenced by prevailing friction conditions which are affected by environmental factors such as humidity and temperature. This study presents a statistical analysis of long-term curve squeal measurements from a curve operated by commuter trains in Sweden. The analysis focuses on the relationship between environmental variables and squeal occurrence, distinguishing between squeal generated on the low and high rail. The results reveal distinct differences in squeal tendencies. Low rail squeal is most likely during relative rail humidity 55%–75%, absolute humidity 7–9 g/m 3 , and temperatures 7–15 °C, with peak occurrence in the morning hours and during the autumn season. The probability decreases notably outside these ranges. A specific range of estimated friction coefficients is also associated with low rail squeal. Conversely, high rail squeal exhibits increased probability during dry conditions and elevated temperatures. Both low rail and high rail squeal probabilities are reduced during low temperatures, rail temperatures close to the dew point, high relative humidity, and during the winter season. The observed differences suggest that separate mechanisms may be responsible for squeal on the low and high rail, involving wheel tread contact on the low rail, and wheel flange or two-point contact on the high rail. The results provide new insights into the environmental dependencies of low rail and high rail generated curve squeal, which can support the development of targeted squeal noise mitigation strategies.