The National Roads Authority (NRA) has acknowledged that a section of the M50 ring road in Dublin will have to close completely for about four nights, most likely before Christmas, as work begins on upgrading overhead bridges into "free-flow" interchanges.
The work at the N4 junction will close the motorway beneath the junction's twin bridges.
It is a move that is likely to cause frustration for late evening commuters and late-night shoppers.
The work has to go ahead before Christmas if a deadline for the introduction of traffic diversions is to be met immediately after Christmas. These diversions will be needed to accommodate the construction of "free flowing" junctions across the N4 interchange. "Free flowing" junctions are designed to allow traffic to move across an interchange without stopping.
Details of the diversions are to be announced by South Dublin County Council this morning.
They will involve northbound M50 traffic heading for Dublin city centre leaving at the N4 Lucan junction and travelling west out to Liffey Valley, where it will do a U-turn and head back towards the city.
The NRA said last night that this arrangement provided for the removal of traffic lights on the junction and the creation of "free-flowing" movement for Dublin-bound N4 traffic as it crosses the interchange.
A separate free-flowing movement will allow traffic coming from Dublin city and destined for the M50's northbound lane to head across the junction unrestrained by traffic lights and on to the N4 road, where it may then do a U-turn before joining the northbound lane of the M50, again unencumbered by traffic lights.
Similar closures of sections of the motorway are expected to occur under the bridges of the Ballymount interchange and the Red Cow interchange as work progresses.
Work on the widening of the M50 and the upgrading of junctions on the western section of the motorway is scheduled to be completed by mid-2008.
However, before this date, work will also begin on junctions at the northern and Sandyford to Tallaght sections of the motorway. These are not scheduled to be finished until 2010.
The NRA has moved to play down the significance of a memorandum issued yesterday by South Dublin County Council which referred to "full motorway closure" of the M50.
The NRA said full closures of the motorway would take place only on sections under interchange bridges and diversions would be put in place.
The authority also said a clause in its planning permission banning certain noisy, night-time works would not apply to cranes lifting bridge decking extensions into place.
