I grew up around the railroad. My dad worked for the railroad for 42 years. I was in the cab of an engine when I was six. I helped dad around the station in Henryetta, OK when I was that age. I loved trains. I have ridden passenger trains from Tulsa to St. Louis and even got my own sleeper. The other day I set out to photograph something railroad related and I remember just how powerful trains seemed to be when I was a kid. Well, looking at the mechanics of a freight car, everything about them says strength, power, durability, etc.
There is nothing fragile about a railroad car. It will be asked to travel millions of miles in all kinds of weather and remain outside for it's entire life cycle.
There is no such thing as a weak link in the coupling device that connect the individual cars and form the train.
Now this is a heavy duty suspension system and there is one between each pair of wheels.