What describes a structure that supports a car body through its center plate?

The correct choice describes a structure known as a span bolster, which is an essential component in the design of freight cars. The span bolster is positioned beneath the car body and is specifically engineered to support the weight of the car and distribute that weight evenly. It acts as a stabilizing structure that connects the car body to the underframe or trucks while allowing for the necessary movement and flexibility during transport.

The design of the span bolster also plays a critical role in maintaining the integrity and structural health of the car, as it ensures that the car body remains properly aligned, especially during turns and when the train is in motion. This component is fundamental to the operation of freight cars within a rail system.

In contrast, other choices represent different components with distinct purposes. For instance, crossover platforms facilitate safe access for crew members between cars or from ground level but are not involved in weight support. Couplers are mechanisms that connect individual railcars to allow for the linking of multiple cars, but they do not directly support the weight of a car body. Truck bolsters, while they are involved in supporting the truck assemblies that bear the car’s weight, do not provide the same centralized support for the car body as span bolsters do.