Car editor Niek Schenk replies: ‘This used to be mandatory in France and some drivers apparently can’t let go of this habit. It was once introduced to indicate to behind and oncoming traffic that you are still overtaking, but will soon be leaving the lane. In addition, you make it clear to any oncoming traffic outside the highways that you are busy with an overtaking manoeuvre. I’ve never heard of this custom occurring in other countries.’
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