A 30km/h speed restriction already in place in parts of Dublin city is being extended to a wider area of the city centre from today.
The new limit will apply to all roads within area extending from Bolton Street on the northside to Kevin Street on the south side, and from Church Street and Bridge Street on the west of the city centre to Gardiner Street and Dawson Street in the east.
Dublin City Council says the decision was taken because dangerous and inappropriate speed is the primary contributing factor to road fatalities.
It claims 45% of pedestrians are killed when hit by a vehicle travelling at 50km/h, but this reduces to 5% when the vehicle is moving at 30km/h.
The Council says the new limit will also help encourage more people to walk and cycle around the city centre.
The move has been opposed by the AA, which says the 'ultra-low' speed limit will pointlessly frustrate ordinary traffic and infuriate careful motorists.
It says 30km/h zones only work when they are engineered properly in traffic-calmed areas, which are self-policing.
The organisation says applying them en-masse on roads engineered for high volumes at flowing speeds is absurd.
The Dublin City Centre Business Association has also expressed concern that the limit may discourage people from shopping in the city centre.
But the Dublin Cycling Campaign has welcomed the new limit, saying traffic congestion and children's safety is set to improve as a result.
It says that the introduction of a 20mph/32km/h limit on some streets in London has cut road injuries by 40%.
Track upgrade works affect DART services
Meanwhile, there are no DART services between Connolly and Grand Canal Dock stations today due to track improvement work in the vicinity of Pearse Station.
Pearse and Tara Street stations are closed as a result.
DARTs are running between Connolly and Howth/Malahide, and between Grand Canal Dock and Bray/Greystones.
Iarnród Éireann is providing shuttle bus services between Grand Canal Dock and the city centre.
All Maynooth and Northern Line commuter services are operating to and from Connolly Station only today.
Connolly-Rosslare Europort services are operating with bus transfers between Connolly and Greystones.
Further information is available on the Iarnród Éireann website.