If a driver moves their arm up and down with short, quick oscillations, what maneuver or intention are they signaling?

Question

DentroTest · Accepted Answer

The General Traffic Regulations establish that the intention to bring the vehicle to a stop or to slow it down considerably (even when prompted by traffic circumstances) must be indicated in advance whenever possible. This warning can be given by repeated use of the brake lights or by extending the arm and moving it alternately up and down with short, quick movements. The other options are incorrect: to signal reversing, the arm is extended horizontally with the palm of the hand facing backward, and to change direction, the arm is kept extended horizontally or bent upward.

If a driver moves their arm up and down with short, quick oscillations, what maneuver or intention are they signaling?

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