Certain people will appreciate using the left turn signal when they don't and the car behind them attempts a pass on the left. They will appreciate it when said passing car impacts them on that left side. If they did not communicate to those behind them that they were turning left then consider buying new cars often (and paying a higher insurance payment). ANY change of direction should be communicated to others, THATS ONE REASON THE DAMN LEFT/RIGHT TURN THINGS ARE THERE.

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