Today's feature is another weird entry in railroad history, the Burlington Northern Boxhopper, or bopper! BN created these prototype cars in order to maximize the use of their rolling stock fleet. Normally, cars are sent out loaded, and returned empty. The aim of these was they could handle boxcar freight one way, and hopper goods on the way back (or vice versa). These cars had retractable floors that were hydraulically powered by a special power car. This way, they could convert between boxcar and hopper on the fly. Unfortunately these aluminum cars didn't work out, and most ended up scrapped. Three of the remaining cars and a power car were donated by the BNSF to the Lake Superior Railroad Museum in 2002.
More info:
https://www.youtube.com/watch?v=jlmyWyI9HT8
Interesting. Never heard of those before.