asked the Secretary of State for the Environment what are the current estimated capacities of new construction road in passenger car units for single carriageway 24 feet, single carriageway 33 feet, and dual carriageway for four and six lanes.
Criteria published in 1974 are concerned with design flows rather than capacities and these are expressed in vehicles instead of passenger car units. In view of the complexity of the subject I will send the hon. Member a copy of Technical Memorandum No. H6/74 on Design Flows for Motorways and Rural All-Purpose Roads which explains the matter fully.Choice within a range is determined by the estimated traffic characteristics of a particular road. The flow levels for motorway and rural all purpose roads are as follows: For a single carriageway—24 ft.—the ranges of vehicles in a 16-hour average day are 12,300–15,000; for a single carriageway—33 ft.—17,700–23,750; for a dual two-lane carriageway 33,700–45,000—all-purpose road—and 45,700–48,000—motorway; for a dual carriageway, three-lane, 50,500–60,000—all purpose road—and 68,200–72,000—motorway.