When you’re turning right from a dual carriageway you should take up your position in the right-hand lane in good time; though not so early that you hold up other drivers. You should be influenced by the amount of traffic; the busier the road, the earlier the change of position should be.
The turn into the central reserve is likely to be a tight one, so make sure that you slow down properly on the approach.
Once you have entered the gap, you need to give way to the left before crossing into the side road. If you have to stop in the central reserve make sure that you straighten your wheels before stopping; this reduces the amount of steering you need to do when setting off again.
You should also cancel your signal at that point otherwise people may think you’re doing a u-turn.
Be careful also that you don’t stop at an angle; or in a position which would prevent a driver emerging from the side into the gap. Unless markings show otherwise you need to treat that small space as a little two-way road; always make sure that you keep to the left of it.
Urban dual-carriageways (those through a built-up area), and those outside of towns and cities, may be national speed limit roads. When you’re driving at speeds of up to 70mph things can change very quickly. You need to think much further ahead and be doubly careful with those mirror checks and lane changes on the approach to your turn-off.
This is an excerpt from Learning to Drive – The Learner Driver’s Manual