Dual Carriage Way Ahead , stay in the left lane until you have had a chance to adjust to the situation and remember to keep a safe distance from vehicles in front.The speed limit on dual carriageways is 70 mph. The examiner will be expecting you to drive at the 70 mph national speed limit if it is safe to do so. If you are behind a slow moving vehicle, overtake if possible.Look well ahead as well as your immediate surroundings on dual carriageways. Traffic that has stopped or reduced speed ahead can be dangerous for fast approaching traffic.