On eastern coal hauling railroads, there were often many grades to be crossed when moving coal from the mine branches to seaport terminals.
When coal is loaded to a car's capacity, it is usually piled somewhat higher than the car sides and heaped along the centerline. As the car is being transported in a train, it rocks, bounces, gets shoved, bucking hard back forth with slack action, and vibrates running on rough faced rail. Some of this action settles and compacts a coal load, but looser coal on top sloughs off over the car sides and ends. This can especially happen at the car ends, with slack action bucking and the higher train speeds becoming more common in the 1930's and 40's. By adding peaks that were a bit taller than the full coal load would be, there was less loss of lading over the car ends from rough handling or riding. On some peaked ends, the ladder side was cutaway for brakeman access over the top of a loaded car.
Notice especially, which railroads most favored these hopper car end extensions. They were prime eastern transporters of export coal that had fairly long runs with many grades over the Appalachians to reach the seaports in long, heavy and fairly fast running trains.
S. Islander