asked the Secretary of State for Transport if he will give an assurance that all trunk road improvement plans will include dual carriageways where peak flows are predicted to exceed 17,000 vehicles per day during a period 15 years from the date of the improvement.

No. A predicted flow of 17,000 vehicles per day is the minimum level at which we would consider a dual carriageway. But the decision on road standard in individual cases depends on a number of factors.