How does downshifting help in decelerating a commercial vehicle?

Downshifting plays a crucial role in decelerating a commercial vehicle by utilizing engine braking. When a driver downshifts to a lower gear, the engine’s RPM (revolutions per minute) increases, which allows the engine to create resistance against the movement of the vehicle. This resistance effectively slows down the vehicle without relying solely on the braking system. This technique reduces wear and tear on the brakes and can help maintain better control of the vehicle, especially on downhill stretches or while approaching stops. By engaging the engine's compression, downshifting aids in bringing the vehicle to a safe speed efficiently and safely.

The other options do not accurately describe the effects of downshifting. For instance, downshifting does not increase the vehicle’s speed, nor is it aimed at making the vehicle more fuel-efficient under typical circumstances. Additionally, downshifting does not prevent a vehicle from going uphill; in fact, a lower gear is often required to climb steep grades and does not relate to deceleration.