Abstract: A lightweight reinforced seat assembly for a transportation vehicle is disclosed which includes a molded seat shell having a shell exterior and a shell interior. The seat shell includes a seat section and a back section joined together by a generally curved section. A plurality of seats is formed in the seat shell. A reinforcing network of longitudinal and lateral, generally enclosed tubular rib elements reinforce the seat shell to eliminate metal framing and weight. The reinforcing rib network includes a front tubular rib element extending laterally across a front width of the seat section, and a top tubular rib element extending laterally across a top width of the back section. Longitudinal edge tubular rib elements extend on opposing edges of the seat shell generally through the seat-section, curved section, and back-section. The edge tubular rib elements are connected to the front and top tubular rib elements.