Boxcars

[John Taylor]

Why did some boxcars have plug doors and sliding doors?

[Tom Kepshire]

John, that is a good question. Boxcars come in two door types, the plug door and the sliding (corrugated) door. They can have one or two doors per side.  Door widths are 10' or 12' for singles and 16' for doubles.  The sliding door system keeps both the weather and direct sunlight out.  It slides using two rollers in a door track and can be opened or closed by pulling on the door handles.  The plug door system closes with a final inward movement (similar to most van sliding doors) that seals the door flush with the interior of the boxcar.  This provides a much better seal than the sliding door boxcar.  A rotating lever on the door activates a gear system to "plug" and "unplug" the door. Found at http://www.alaskarails.org/fp/Boxcars.html

[Steve Dolzall]

 In a conventional car, the plug door provides the car contents far better protection from the effects of the elements while in transit than would be possible with a sliding door car. In the case of an temperature controlled car (insulated or refer) the plug door design allows a level of temperature control not attainable with a sliding door car.

[Tim T Swan]

I think it's mostly the result of modernization and progress.  In steam or pre-WW2 days, virtually all boxcars had sliding doors, in single-door sizes from 6-feet to 8 feet wide  In the 50's, plug doors began appearing on new boxcars so that by the 60's almost all boxcars were being built with plug doors.

[Geof Burns]

I would think that a sliding door would not keep the weather out very well, so anything that could be damaged by water would be better off in a Plug Door car.