Road safety continues to be an important issue, particularly on national primary single carriageway roads in Ireland.  Any new measures that help reduce accidents and fatalities on single carriageway roads must be further advanced.  To this end, a working group comprising representatives from National Road Authority, Regional Design Offices, Local Authorities and Consultants has been researching a new road type for the last two years.  The view of the group is that the 2 plus 1 road has potential for use in Ireland because of the poor accident record/characteristics of single carriageway roads and because of the traffic volumes on much of the National Primary network.  It is proposed to pilot four 2 plus 1 schemes around the country over the next few years. 

A '2 plus 1' Road

A 2 plus 1 road consists of two lanes in one direction of travel and one lane in the opposite direction.  The two-lane section, which provides a safe overtaking zone, alternates with a one-lane section at intervals of 2km approximately.  The traffic streams are separated by a safety barrier system, which prevent overtaking manoeuvres on the one-lane section.  Right turning movements will be at controlled junctions and a reduction of head on collisions is anticipated. 

Sweden has led the way in research and development of the 2 plus 1 road type with safety barrier systems and has constructed in excess of twenty-five such schemes since 1998, both on green field and retrofit sites.  2 plus 1 schemes also operate in Finland, Denmark, Scotland and Germany.  The National Roads Authority in conjunction with several Local Authorities propose to pilot a number of 2 plus 1 schemes around the country in the near future.  At present many National Primary roads have climbing lanes with two lanes on the uphill section and one lane on the downhill section.  Irish drivers are familiar with their operation, notably the reduction from 2 lanes to 2 lane beyond the crest of a hill.  Therefore, the main difference between these roads and the new 2 plus 1 road type is the existence of a safety barrier between the opposing traffic streams. 

The 2 plus 1 road type will be considered for new National Primary projects, on routes to which the high quality dual carriageway/motorway standard does not apply.  This applies to approximately 700km of new projects, with a potential of retrofitting an additional 150km on existing routes.  Therefore this road type potentially applies to thirty per cent of National Primary roads.  
 

Proposed Road Standard following completion of the national primary programme as outlined in NDP

Road Type	Length
Standard 2 lane	750km
2 plus 1	850km
Motorway or Dual Carriageway	1200km

 
The main advantages of using the 2 plus 1 road type:-

The main advantage of 2 plus 1 roads is enhanced safety.  The separation of opposing traffic streams in a 2 plus 1 road prevents cross over accidents including head-on collisions. 

In Sweden, it has been estimated that a 2 plus 1 road type with a safety barrier led to an overall reduction of 50% of fatal accidents when compared to a single carriageway road.  This was achieved largely by the elimination of head on collisions and a transfer of accidents from the fatal category to the minor injury category.  (Bergh, Carlsson, 2001)

Therefore, the primary benefit of the 2 plus 1 is the overall reduction in the severity of accidents in comparison to the single carriageway road.

The provision of overtaking section every 2 km reduces driver frustration and the provision of a central safety barrier eliminates imprudent overtaking.  Provision for right turning movements will only be at designated junctions. 

Analysis of the economics of two-lane roads has indicated that the 2 plus 1 is a slightly more economic solution than the wide single carriageway. 

Introduction of the 2 plus 1 road type in Ireland

Initially there will be four pilot projects on national primary roads.  These 2 plus 1 projects are as follows:

Location	Description
Co. Cork N20 Rathduff to Mallow	Retrofit 9km
Co. Leitrim N4 Dromad-Roosky	Green field site 8km
Co. Monaghan M2 Clontibret to Castleblaney	Green field site 15km
Co. Donegal N15 Ballybofey to Stranorlor	Green field site 16km

These projects will allow for the traffic, operational and safety assessments of the 2 plus 1 road type in Irish conditions.  Driver behaviour and attitude will be monitored as well as accident characteristics. 

According to Sligo County Council's Senior Engineer Tommy Carroll, 'The introduction of this type roadway to our national road network has huge safety benefits.  This should result in a significant reduction in deaths and serious injuries on our roads at local and national level.'

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