We can complete the sentence as follows: 1) Giving a turn signal when you initiate the turn allows the vehicles behind to adjust their speed in time.
When you should give a turn signalYou should give a turn signal when you initiate the turn. This immediately alerts the other road users likely following behind you to apply caution as they approach a turn.
Giving this signal on time ensures that all are made aware and not taken by surprise when you eventually make the turn. So, the signal should be given when you initiate a turn.
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