Milwaukee also tried the wind resistance idea -- they built hoppers designed
with a top that was mechanically closed as the train slowly rolled. The cars had
these big 'arms' sticking up IIRC.

This wasn't so much for wind resistance as for the fact that the S.D.
coal being hauled in these cars is little more than burnable dirt, and
that a significant fraction would be lost to the wind in transit if
they weren't capped. However, I don't believe much of this coal was
hauled out during the Steam Era.

--
david d zuhn, St Paul Bridge & Terminal Ry., St. Paul, Minn.
http://stpaulterminal.org/