§ Mr. MarlowTo ask the Secretary of State for Transport what is his estimate of the maximum capacity of an existing three-lane motorway without delays in the overtaking lane under(a) present driving patterns, (b) an enforced 70 mph speed limit and (c) an enforced 70 mph speed limit with gaps between vehicles, as recommended in dry conditions, being observed.
§ Mr. Peter Bottomley[holding answer 7 July 1988]: The maximum capacity of any road will vary with the vehicle mix, road layout, time of day, time of year and driving conditions.
The Department produces guidelines on carriageway standards in relation to traffic flows only for the purpose of establishing which options should be appraised. As a starting point for assessment, dual three-lane standard will be considered for a rural motorway if the forecast average annual daily traffic flow in the design year, 15 years after the road opens, is in the range 50,000–79,000 vehicles. The design flow for any road is less than its maximum capacity.