Train Operator Practice Exam

In the context of subway systems, air compressors play a crucial role in various functions, including operations that necessitate compressed air like train braking systems and systems that require pneumatic operation. These compressors typically rely on the power supplied through the third rail, which is the primary source of electric power for train operations.

When the power supply from the third rail fails, the air compressors lose their primary power source. This loss of power means that they can no longer function since they are not equipped with independent power systems or backup systems to operate during such failures. Hence, without any power supply, the compressors will not operate at all. This can have significant implications for the safety and operation of the subway system, as compressed air is essential for safe braking and other pneumatic needs.

In contrast, other possible scenarios like operating on backup power or intermittently would imply some level of functionality despite the failure of the primary power supply, which is not the case under typical conditions for subway air compressors.