One of the problems with the adoption of the covered hopper was that both the loading and unloading sites had to be set up differently for covered hoppers as compared to loading and unloading boxcars. My guess is that it was a chicken or egg problem. Customers could not convert as the railroads did not have hoppers to supply and the railroads did not want to convert to covered hoppers because their customer's sites could not handle them.
As late as the late 1980s UP (MP) still had customers who could not unload covered hoppers and they had to move bulk beans in boxcars.
