Recent advancements in buff and draft testing techniques

A new method for evaluating the curving stability of any freight railway car under buff and draft conditions is described. A special test vehicle was designed and constructed by the Association of American Railroads (AAR) for the purpose of applying controlled levels of lateral load at the coupler pin of any adjacent car and while in motion. This test vehicle is used in determining the maximum lateral coupler load that can be safely applied to any candidate car under various curving and speed conditions. Analytical methods are also developed for predicting the coupler angles and forces generated under any given buff or draft conditions, track curvature, and coupling arrangements. The proposed method combines testing with analysis in order to determine the level of buff or draft force at which the lateral coupler load test limits are exceeded. As an example for the method, the developed techniques are used to examine the curving performance of a standard 89-ft flatcar when coupled to another relatively short 2-axle flatcar. The results indicate that the coupling of the two cars reduces the curving stability of the long flatcar under realizable buff and draft conditions