c. Flatcars. Flatcars are used for loading items whose dimensions cannot otherwise be
accommodated and where protection from the elements is necessary. The way in which loads are
secured is extremely important for loads on flatcars. Flatcars are built in a variety of lengths from
40' up to 89' and capacities of up to 125 tons and more for limited use special service cars when
there are more than four axles on the car.
d. Hopper Cars. Hopper cars are built in both covered and uncovered variations. Bulk
items such as coal and iron ore are appropriate for open top hoppers. Covered hoppers are used
for commodities such as grain or plastic pellets where environmental contamination and
protection are necessary. These cars come in a variety of lengths up to 55' and 125-ton capacity.
e. Gondola Cars. Gondola cars are essentially flatcars with sides. They are used for
such commodities as pipe, scrap metal, and fabricated steel items. Gondola cars are used for
commodities where environmental contamination and protection from the elements are not
necessary. The method of loading and unloading is a factor in their use.
f. Intermodal Container Cars. Intermodal container cars are long flatcars designed
especially for carrying either piggyback trailers or containers, sometimes called a "TOFC/COFC
car." Intermodal cars are equipped with container pedestals and sometimes piggyback trailer
Freight railcars are comprised of the basic elements as shown in figures 2-2, 2-3, 2-4A, 2-4B and
a. Center Sill and Stub Sill. The center sill is the backbone of the car. It is the main
structural element for carrying the loads of the individual car. The center sill also transfers the
various longitudinal forces encountered during train operations from car to car. Some tank cars
whose design utilizes the tank itself to transfer and carry the various loads usually handled by the
center sill have what are called stub sills instead of a center sill.
b. End Sills and Body Side Sill. End sills and side sills run along the end and sides of
the underframe and provide structural integrity to the car and reinforce the center sill.
c. Cross Bearers and Cross Ties. The cross bearers and cross ties run perpendicular to
the center sill and transfer loads from the deck to the center sill.
d. Body Bolsters and Body Side Bearings. The body bolsters which also run
perpendicular to the center sill provide the connection between the railcar's center sill and its
trucks. The loads are transferred from the body bolster to the truck at the center plate with side
bearings providing stability.
e. Coupler. Couplers transfer forces between the car and the freight cars or locomotive
coupled to it. The coupler is comprised of a shank, head, and knuckle. The shank is secured to
the draft system, and the knuckle is used to couple to other knuckles on other freight cars.
Although there are several types, all couplers used in interchange in the United States and on all
Navy railcars will interlock. See Figure 2-4A and 2-4B for illustrations of coupler components.
See Figure 2-5 for an illustration of different coupler types.