What does the master control handle regulate in a train?

The master control handle is primarily responsible for regulating the speed and acceleration of the train. It allows the train operator to make adjustments to the train's throttle, essentially dictating how much power the train's engines will produce. By moving the handle, the operator can increase or decrease the speed of the train as needed. This control is crucial for managing the train’s performance, especially when navigating through varying track conditions, making stops, or accelerating as necessary.

Other systems, like air pressure in the braking system or power supply to passenger cars, are independently regulated through separate controls and mechanisms, while lighting conditions within the cabin are handled by electrical systems separate from the train's propulsion and speed control.