A lightweight hopper car that includes one or more reinforcing members at specified locations, so that the hopper car has both a carrying capacity and a structural strength comparable to those of existing, heavier hopper cars. Specifically, the present application discloses that the hopper car may be reinforced at one or more locations including (i) at selective intersections between the center sill and slope sheets of cargo wells; (ii) between side slope sheets of adjacent cargo wells; (iii) at the junction between the side sheets and end slope sheets of the hopper car; and (iv) along the end combing seal between opposed carlines, if the hopper car is covered. In addition, the present application discloses a novel means of reinforcing side sheets of a rail car, including hopper cars, against the warping that commonly occurs when welding the side sheets at the car is fabricated.