Hunting of rail vehicles refers to self-excited oscillation of truck and carbody. This dynamic instability is due to the conicity of the wheels, the wheel/rail creep forces and the action of the suspensions. Hunting increases wheel/rail wear, causes damage to sensitive lading and in extreme cases can throw the track out of geometry. Furthermore, severe hunting can create unsafe operating conditions that lead to derailments. Although it is widely recognized that truck hunting is not a good thing, it is a fact that many thousands of trucks do hunt on any given day but the number of derailments from hunting are few. So when is the hunting unsafe? Database and parametric studies of unsafe hunting are presented in this paper. The FRA database was used to study the hunting derailments by year, car type, track, speed, load condition, weather and temperature. Parametric studies of hunting and unsafe hunting of three-piece freight cars were conducted based on a large number of measured wheel profiles in combination with worn and new rail profiles. The vehicle, track and operational factors that have the major influence on unsafe hunting are analyzed and the conditions of unsafe hunting presented.

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