When did this type of car come into general use? Thanks
The earliest ones that survived to recent times were built for the Northern Pacific in 1969 (last seen as NOKL cars). The shorter cars with the “opera window” partitions" were built for a few customers (UP, BN, MILW) in early 1977; not until 1983 were more ordered by BN and Trailer Train. After that, the design was ordered fairly often, and other builders made close copies (Thrall had patented the original Center-Beam cars). It was in about 1986 when the more open divider (same strength, less tare weight) came about, as well as the more usable 73-foot inside length.
Since the superstructure takes the place of a heavily reinforced center sill, the cars are top-heavy. That, together with the long drawbars necessitated by their length, make them among the most derailment-prone cars around (and that doesn’t even mention the tipping hazard if they’re loaded or unloaded improperly).
Edited later in the evening to provide more precise dates.
You sure don’t go very fast when you have an 11000 foot train of them in the wind and only have two units!