Look at the picture, in the very link you posted. There are gons, in the picture, not hoppers. Gons carry sludge, and contaminated soil, etc,(usually damp, or wet, therefore, heavy. Garbage is usually "dry", therefore, lighter) and are "tarped", to prevent the contamination from blowing away. The garbage cars, are hoppers, or converted boxcars. CoalPorters, CoalTainers, etc., of the "bathtub" variety, are hoppers. Traditionally, high-sided open top cars, are hoppers. Low sided, open top cars, are gons. Hoppers used to have operating doors on the bottom, for discharging product, but seem to be optional now.
Again, say what, say what, say what? Am I arguing with a yardmaster here (with or without mice in his pocket)?
OK, first the AAR classifies all hopper cars as being self-clearing (which generally doesn't require illegal immigrants with shovels, but does require doors in the bottom), as seen here:
(cited 2002 ORE Register)
have fixed bottoms (no doors in the floor), as you can see in the listing linked above, but some classes do have doors (apparently hinged from the center sill - I always thought these were mainly used for MOW purposes). Oddly, the GW classification seems to apply to double stack intermodal cars. But anyway, high side, low side, whatever if it has an open top, fixed sides, and fixed bottoms, like the ones in the accident photo linked on the first page seem to do, then it's a Gon.
Also note, the manufacturer TrinityRail calls its coal car with bottom hoppers a 'Hopper Car', and it's fixed bottom coal car a 'Rotary Gondola', while Freightcar America has this to say:
The AeroFlo™ BethGon Coalporter® is a member of the Coalporter line of lightweight, high capacity coal cars. ...
FreightCar America's double twin tub floor design adds up to 21 tons of capacity over conventional steel gondola cars
Kinda why they named it Bethgon and not BethHop.
Even better, here's the FreightCar America product page for woodchips and municipal waste http://www.johnstownamerica.com/product ... odchip.htm
- they call it a gondola, even with the half round bottom tub extensions (which don't have doors). On the same page, they also offer a woodchip hopper, which has - hopper doors!
Diagrams are included for both for your reading pleasure.
So, to sum up - hoppers have...bottom hoppers, and gondolas don't.
If, in the picture, those were really rebuilt Hoppers NOT sporting a G classification, then of course I will stand corrected - but I'm thinking they are classed as gondolas (well, were - some are probably classed as scrap metal by now)