If a rail car had a cylindrical tank and a covered dome containing all the fittings and valves, it would be classified as a ________ rail car.

• A. Boxcar
• B. Non-pressure tank
• C. Cryogenic liquid
• D. Pressure tank

Answer: (D)

The key idea is recognizing how fittings and valves are organized on the tank car and what that implies about what it’s designed to carry. A cylindrical tank with a covered dome that houses all the fittings and valves is built to handle products under pressure. That enclosed dome protects and centralizes the pressure-relief devices, gauges, and connections needed to safely manage the cargo’s pressure. This setup is the hallmark of a pressure tank car, which is specifically used for gases or liquids that are stored or transported under pressure.

Non-pressure tank cars carry liquids not under pressure, so they don’t rely on an enclosed dome for fittings in the same way. Boxcars are a different freight type altogether (not a tank car), and cryogenic liquid cars are designed for extremely low temperatures and have insulation features; their distinguishing factor isn’t the dome containing fittings. So the correct choice reflects the car’s purpose to transport pressurized contents.