In recent years much effort has been expended within the industry on investigating the causes of truck lateral instability or hunting. To determine the cause of this phenomenon various research organizations, among them the Association of American Railroads and Arizona State University have performed comprehensive tests to validate mathematical models which can be used to conduct parametric studies. These models allow for investigating various means for alleviating the non-linear instability problem. In addition, much effort has been expended by a number of private companies to develop freight car trucks with superior hunting performance. It is now well understood by the railroad industry that, given the current state-of-the-art in freight car truck design, some truck hunting behavior is unavoidable. Less attention, however, has been directed toward determination of what amount of truck hunting, if any, is acceptable. This paper describes the results of two field investigations in which truck hunting instability led to either excessive wear or structural degradation. Various means readily available to the industry were then investigated as to their effectiveness in controlling hunting. Results are presented showing that the particular problems encountered were avoided by control of the hunting phenomenon rather than its complete elimination.

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