High-quality Dual Carriageway - Specifications

Specifications

Standard motorways: 52,000 vehicles AADT - annual average daily traffic. The road type is all-purpose dual carriageway (D2AP), but with the same specifications as motorway: a carriageway width of 7 metres (23 ft) and a hard shoulder of 2.5 metres (8 ft 2 in) width. HQDCs are limited access (grade-separated junctions only) and not intended to have junctions with minor roads. Junctions with major roads are grade-separated and to motorway standards.

All HQDCs in Ireland currently form part of national primary roads, and therefore use the national road speed limit of 100 km/h (62 mph). There are exceptions however, as special speed limits may now be specified for sections of road if the local authority passes a by-law. For example, a section of the N1 from the northern end of the M1 motorway (north of Dundalk to the border with Northern Ireland) has a 120 km/h (75 mph) speed limit.

Signage on Irish HQDCs is similar to signage used on Irish motorways, and junction numbers may be present (as on motorways, indicated by a white number on a black panel in the corner of signs). However signage on HQDCs uses a green background instead of the blue background used on Irish motorway signage. In the event of an HQDC being a regional road, black text on a white background would be used instead. Also, as on other all-purpose roads, signs should include patches for roads of other classifications (on motorways, all information signage should have a blue background).

As high-quality dual carriageways are not motorways, they do not need to conform to motorway regulations, therefore slow-moving vehicles (e.g. tractors, farm vehicles etc.) as well as cyclists are permitted to use these roads. HQDCs have a hard shoulder marked with a broken yellow line (as is standard on Irish roads), rather than the solid yellow line used to mark the hard shoulder of an Irish motorway. Also, L-Drivers (Learner Drivers), who are not permitted to drive on motorways can do so on high-quality dual carriageways, as on the rest of the national road network. HQDCs are a road type, not a classification, and the normal rules and regulations applying to all-purpose roads apply on HQDCs.

Lay-bys (rest stops) are permitted on HQDCs and the N6/M6 Kinnegad - Kilbeggan scheme originally featured lay-bys, which would not be legal at present on roads with full motorway status, prior to its redesignation as a motorway. The M9 Carlow bypass was built with lay-bys as it was originally to be built as an HQDC section of the N9 route. The lay-bys were removed after the road was reclassified as a motorway. Lay-bys on other HQDCs which were reclassified as motorways were restricted to authorised vehicles only and are likely to be used mainly by Garda Síochána (police) patrol vehicles.