NRA decides against '2+1' road design

The National Roads Authority has decided not to use a "2+1" road design for an upgrade of more than 850km of national roads.

The system is designed to eradicate head-on crashes by providing overtaking lanes at 2km intervals in a bid to curb driver frustration and has been piloted on three national routes over the past two years.

The "2+1" layout has two lanes in one direction, and one in the opposite. The two-lane section is a safe overtaking zone and alternates with the one-lane section at intervals of around two kilometres with a barrier separating traffic. Separating lanes of oncoming traffic is one of the recommendations in a draft of the new Road Safety Strategy 2007 to 2011.

However, the NRA found that there was a tendency for drivers to accelerate to try and pass traffic just before the double-lane section switched and that this was a hazard.

A cost-benefit analysis also showed that an upgrade on a single carriageway national route to a 2+2 - with two lanes in each direction separated by a central barrier cost - between 10 to 15 per cent more than a 2+1 format.

Because the 2+2 arrangement can also carry more traffic at 20,000 vehicles per day, compared to 14,000 for a 2+1, the NRA has decided to use this design layout as the basis for the widening of almost 850km of single carriageway national roads.

An NRA spokesman said the existing stretches of 2+1 developed during the pilot scheme would be left unchanged, and the design would remain as an approved option.

"The NRA board has decided that from a cost benefit standpoint and to avoid traffic coming into conflict, a 2+2 configuration will be used. This design also offers additional traffic capacity on these routes." The 2+2 road layout differs from a standard dual carriageway in that it does not have a hard shoulder.

The NRA is also understood to be seeking to restrict access from private houses and business on to roads due to be upgraded to 2+2 designs.

Although national roads account for just 6 per cent of the road network, they account for 42 per cent of fatal collisions, and 35 per cent of fatal collisions in which speed is a factor. These roads carry almost half the daily traffic.

Four out of five fatal crashes on national routes are outside built-up areas.

According to the NRA, there have been no serious crashes on the 2+1 roads used in the pilot study.

Among the routes piloted was a nine kilometre stretch of the N20 between Mallow and Rathduff, Co Cork; some 15km of the N2 between Clontibret and Castleblayney and a portion of the N24 between Piltown and Fedown.

When testing of the system started in 2005 it was planned to convert about 20 per cent of the State's road network to the 2+1 format over the next decade.

The 2+1 layout was pioneered in Sweden, where more than 950 kilometres of road have been retrofitted. Research from Sweden suggests a 50 per cent reduction in fatal crashes, and that the remaining crashes are less severe.

Approximately 20 per cent of all crashes are head-on collisions, and they are responsible for almost two in five of all fatalities.

The NRA was unable to provide an up-to-date cost estimate for upgrading single-lane dual carriageway routes to 2+2.

In 2005, it was estimated that a new 2+1 road would cost around €4 million per kilometre, while an estimate of an upgrade of an existing road was estimated to cost around €400,000 per kilometre.