§ Mr. Warren
To ask the Secretary of State for Transport what are the average annual daily traffic flows required by his Department to justify dual carriageways on trunk roads; and if he will list the dates and numbers by which this figure has been increased during the last 40 years.
§ Mr. Peter Bottomley
The justification for trunk road schemes is based on a comprehensive appraisal of costs and benefits, not simply on traffic flows. The Department produces guidelines on carriageway standards in relation to traffic flows only for the purpose of establishing which options should be appraised. Dual carriageway standard will be considered for a rural trunk road if the forecast average annual daily traffic flow in the design year, 15 years after the road opens, is in the range 11,000–46,000 vehicles.452W
The guidelines reflect the costs and benefits of the different carriageway widths during both normal operating conditions and maintenance. They also take account of the performance of modern vehicles and road design. Earlier figures were not produced in the same way and are not properly comparable.