Final answer:
A pressure tank railcar is characterized by being thick walled with large lumens to handle high pressure, and they lack valves to mitigate leakage risks.
Step-by-step explanation:
A distinguishing characteristic of a pressure tank railcar is d. thick walled, large lumens, high pressure, lack valves. These types of railcars are specifically designed to safely transport liquids or gases that are pressurized.
The thick walls and large lumens are essential for withstanding the high pressure without needing external valves, thereby reducing the risk of leaks or accidental release of contents during transport.