If a driver intends to slow down or stop, what signal should they use?

When a driver intends to slow down or stop, using a stop signal is the appropriate choice, as it effectively communicates their intention to other road users. A stop signal is typically executed by extending the arm out at a right angle with the palm facing downward or using the brake lights of the vehicle, which serves as a clear warning to other drivers and pedestrians that the vehicle is about to reduce speed or come to a stop. This action helps prevent accidents by ensuring that others are aware of the driver's intentions.

The other options either do not convey the correct message regarding slowing down or stopping or are irrelevant in this context. An arm signal to the right or left suggests a turn, while a speed-up signal implies an intention to accelerate rather than decelerate. Therefore, using a stop signal is the most effective method of notifying others on the road that one is about to slow down or come to a stop.