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Why are freight train cars wheels/axles always detached in accidents?

Why is it every time I see freight trains in accidents that the freight car wheels/axle assembly is detached from the axle truck? Do the cars just sit on the axles and the axles are not secured to the wheel truck?


The wheel and axle assembly sit on the track. The truck assembly sits on the wheel/axle assembly. The truck has a bolster pin, which is a vertical pin sticking up from the centre, that fits into a hole in the carbody. There is no actual device that secures these pieces together - it's only their immense weight that keeps them together. But, except for big wrecks and repairs, they stay together rather well.
Actually the AAR (Association of American Railroads) rules require the car no stenciled on either both sideframes or the bolster of each truck (or bogie). Every wheel is marked by the shop the mounted it, and every bearing is marked by the shop that mounted it and the date. Since shops must keep records, it is very easy to trace the history of a wheelset. In addition, the castings are marked by the manufacturer, dated, and pattern numbers. Thus if a manufacterer produces faulty products, they can be recalled quickly, and the manufacturer held accountable. In theory anyway. The last major recall was of castings made by a manufacturer that was out of business by the time failures were occuring.

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