The presence of one or two ladders is a matter of who built the cars and who would use them, ditto the presence of safety railings and platforms. Some car owners or lessors would specify certain safety equipment while others would not. The same is true for the valve and fitting arrangement. There are certain regulatory requirements that have to be met, and those requirements have changed over the years, but once past those requirements tank cars tend to reflect the users preferences. Part of this is the change in the uses of tank cars. Prior to WWII petroleum products were the primary products being carried in tank cars. After the war more specialty chemicals came into use thus requiring certain subtle changes to what otherwise would appear to be the same sort of tank car.
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