So that traffic behind you is able to anticipate your turn, and can act accordingly.
You should use your turn signal in far enough advance so the car behind you knows you are going to turn and has enough time to slow down. However, putting the turn signal on too far in advance can be confusing because the following car will not know exactly when you are going to turn.
In New Jersey, you should signal your intention to turn at least 100 feet before making the turn. This gives other drivers adequate notice of your actions. Additionally, it's important to use your turn signal continuously until you complete the turn to ensure clear communication with other road users.
To properly use the bike left turn signal while riding on the road, extend your left arm straight out to the side to indicate your intention to turn left. This signal should be given well in advance of the turn to alert other road users of your intended maneuver.
Reason number one - it is a law. Reason number 2 - it allows other drivers, pedestrians, and cyclists to know what your intentions are.
Slow down and turn your low beam headlights on. Turn on signal lights in advance and brake early as you approach a stop.
No.
Every time you turn left or right, or switch lanes on a highway you should use your turn signal in your car.
When merging, you should use a turn signal. In any situation in which your movement could affect another car, you should signal. Not to do so is a moving violation.
To properly use the turn signal on your bicycle, extend your left arm straight out to indicate a left turn, and extend your right arm straight out to indicate a right turn. Remember to make these signals clearly and in advance of your turn to alert other road users.
To allow others [drivers and pedestrians] to know what we intend to do.
Use your turn signal to both pull out of and return into the lane. Motorists should not signal their intention to pass by flicking their high beams.