Final answer:
When a train is disabled, mechanics are the most suitable employees to assist because they have the expertise to diagnose and fix a wide range of mechanical issues that can occur with trains, including those related to electrified transportation systems like overhead lines or third rails.
Step-by-step explanation:
If a train crew requires assistance to move a disabled train in passenger service, the employees who could help the crew most would likely be mechanics. Train mechanics have the expertise to diagnose and fix mechanical issues that may cause a train to become disabled. This can include problems with the train's engine, brakes, or other mechanical systems that are vital for the operation of the train. Given the context provided about electrified transportation systems, where trains can be driven electrically via overhead lines or a 'third rail,' it is essential that mechanics understand how these systems interact with the train's overall mechanics to ensure proper function.In contrast, while electricians, signalmen, and track maintenance workers play critical roles in the overall running of a rail system, their expertise is more specialized. Electricians might be called upon if the issue was specifically related to the electrical systems that are connected to the wired systems mentioned, but they may not be equipped to handle broader mechanical failures. Signalmen focus on the signals and train control systems and track maintenance workers concentrate on the physical condition of the tracks, neither of which would be directly involved in repairing a disabled locomotive unless the issue pertained to their specific area of expertise.