Mechanism of squeal noise generated by trams

Squeal noise is very often the most disturbing noise source of railway systems in older cities. At present the effect of measures to reduce or to eliminate squeal noise cannot be predicted and seems to be influenced by a large number of dependent parameters. On the basis of the measurement results of a research project in three cities with seven different tram types on various types of rail structures the influence of the most important parameters on the occurrence and the noise level was analyzed. The analytical model for squeal noise, developed by Rudd [1], was confirmed by these results. However, the model appeared to be incomplete for the influence of the rail structure such as roughness and dynamic properties. Furthermore, the model overestimates the amount of damping in the wheel which is needed to eliminate squeal. Additional knowledge is needed about the change of friction coefficient with lateral creep and about the dynamic properties of resilient wheels.