In locomotive propulsion, what is notching and why is it important for speed control?

• A. Changing the locomotive's direction.
• B. Selecting a throttle notch to control power output and speed; used in DC locomotives.
• C. Engaging automatic brake release.
• D. Monitoring wheel slip.

Answer: (B)

Notching means selecting a throttle notch to set the propulsion power in discrete steps. Each notch provides a specific level of voltage or power to the traction motors, so the engineer can increase or decrease power in defined increments to control acceleration and speed. This stepwise control is why speed management is smooth and predictable on DC locomotives—you can climb from standstill to cruising speed by moving through the notches, adjusting for load and track grade without overshooting.

Chances are you’ll hear this tied to the throttle control on DC locomotives, where the notch positions explicitly determine how much power the motors receive. The other options aren’t about setting propulsion power: changing direction uses a separate control, automatic brake release belongs to the braking system, and wheel slip is a safety/traction monitoring function rather than a throttle setting.