What are cryogenic tank cars primarily used for?

Cryogenic tank cars are specifically designed to transport refrigerated liquefied gases. These gases, such as liquefied natural gas (LNG) or liquid oxygen, must be kept at extremely low temperatures to remain in a liquid state. The insulated construction of cryogenic tank cars helps maintain these low temperatures, preventing the gases from vaporizing and ensuring safe and efficient transport.

The other options, while relevant to freight transport, do not align with the primary function of cryogenic tank cars. Solid granule materials and bulk cargo like coal are typically carried in different types of rail cars that are not designed for the specialized requirements of cryogenic gases. General freight encompasses a wide range of goods, but it does not specifically address the unique needs of transporting refrigerated liquefied gases, which is the distinctive purpose of cryogenic tank cars.