noun
conductor's compartment
A small room or compartment on a train where the conductor works, typically located at the end of a car.
車掌室のドアには「関係者以外立ち入り禁止」と書いてある。
The door to the conductor's compartment says 'Authorized Personnel Only'.
運転室 is the driver's cab (front of the train), whereas 車掌室 is the conductor's compartment (often at the rear or middle).
Compound of 車掌 (conductor) + 室 (room, compartment).