Originally Posted by wsbob

As general advice, a cyclist turning their head to look at traffic in the adjacent lane is not a sufficient signal to persuade a driver in that lane to slow down to let the cyclist into that lane, especially if the signaling effort is limited to that action alone. A cyclist turning their head to check for traffic possibly present to the side and behind them can be a very slight, brief, easily indiscernible or completely overlooked action, nothing nearly as clearly visible as an arm extended, held out for a period of time, say 3 seconds or more to indicate intention to turn, slow or stop.

I believe a basic good procedure is as follows: 1. Turn head and eyes to look for traffic. 2. Return head and eyes straight ahead, extend arm to indicate intention for at least 2 seconds and longer if possible. 3. For turns, after displaying the signal for a minimum of 2 seconds, Look to the side or back again to see if the way is clear, and if it is, return hand to the bars and immediately commence to begin the intended action.