Mr. Wm. Rossasked the Secretary of State for Northern Ireland what is the normal radius of a curve on a dual carriageway and on a single carriage trunk road, respectively, in Northern Ireland where the change of alignment is 10 degrees, 20 degrees, 30 degrees, 40 degress, 50 degrees, 60 degrees, 70 degrees, 573W 80 degrees and 90 degrees; and what is the minimum allowable radius at each such change of alignment.
§ Mr. CarterThe radii of horizontal curves on rural all-purpose dual carriageways in Northern Ireland are normally substantially above the minimum desirable which is 825 metres, where the absolute minimum allowable is 465 metres. Equivalent figures for single carriageways are 650 metres and 400 metres respectively. The minimum radius is not controlled by the angle of change of alignment. Where this angle of deviation is large it is usual for the requirement for forward visibility to outweigh minimum radius as the governing design factor.
Mr. Win. Rossasked the Secretary of State for Northern Ireland at what density of traffic his Department specifies a dual carriageway.
§ Mr. CarterOn current Department of Transport standards which the Department of Environment for Northern Ireland follows, a dual carriageway becomes justified when the traffic flow rises above 17,000 vehicles per day. Exceptionally these standards are not applied, for example, where, because of terrain, construction of a dual carriageway would prove no more expensive than single carriageway construction.