A seat for a transportation vehicle has a rigid seat cushion structure and a rigid seat back structure. The seat back structure has two rigid side parts and upper and lower crosspieces connecting the side parts. The upper crosspiece connects the two side parts to each other in the region of their upper ends, and the lower crosspiece connects the two side parts at a distance from the lower ends. The lower crosspiece is above that region of the rear part that supports the posterior of the occupant. The arrangement of the lower rigid crosspiece holds the posterior of the occupant between the lower crosspiece and the seat cushion structure. Thus, the occupant's back and head are not moved up, in particular are not moved beyond the region of the head restraint of the rear part.