What mechanical component does a train operator manipulate to engage the brakes?

The brake handle or pedal is the correct choice because this component is specifically designed for the train operator to control the braking system of the train. When the operator engages the brakes using this handle or pedal, it activates the braking mechanism, which is crucial for slowing down or stopping the train safely. This component allows for precise control, necessary for managing deceleration in various operating conditions and ensuring passenger safety.

In contrast, the signal lever is used to communicate signals to other trains or to switch tracks, and the throttle control regulates the speed of the train by managing engine power. The coupler release is used for attaching or detaching train cars, not for manipulating the braking system. Understanding the function of each component is essential for effective train operation and ensuring overall railway safety.