The 30kph speed limit zone proposed by Dublin City Council makes "no sense", say critics.
The new limit comes into effect on Sunday and will now apply from Bolton Street in the north inner city to Kevin Street Lower and St Stephen's Green on the other side of the Liffey.
It will also extend from the Church Street and Bridge Street areas in the west to Gardiner Street, Tara Street and Dawson Street on the east.
And it will operate 24 hours a day -- taking in periods when there is very little traffic on the roads.
The limit is being imposed on busy roads like the North and South Quays, Parnell Street, College Green, Dame Street, Dawson Street and Kildare St.
AA director of policy Conor Faughnan said there was " just no sense" in expanding the 30kph area, adding the move would infuriate motorists.
He said applying the lower speed limit "en masse" on roads that were engineered for high volumes at flowing speeds was "absurd".
"In road safety terms, Dublin City is one of the safest places in the country. The road safety justification does not exist and nor is there any reason to believe an assertion that a 24/7 30kph limit will improve traffic flow," Mr Faughnan said.
The Dublin City Business Association (DCBA) said the speed limit was appropriate for the main pedestrian streets like Clarendon St and South William St, where there are lots of cafes and bars.
"In areas like the quays and St Stephen's Green -- the main transit routes in and around the core of the city area -- such a low limit is probably inappropriate," the DCBA told the Herald.
A council review of accident statistics for the Dublin city area between 1998 and 2007 showed 47pc of fatalities and 24pc of people injured were pedestrians.
The local authority also pointed to research showing that 45pc of pedestrians died when struck by a car at 50kph but the fatality rate was only 5pc when hit at 30kph.
The Lord Mayor of Dublin, Emer Costello, is in favour of the plan.
She said it was "well recognised" that inappropriate speed was the "primary contributing factor to road fatalities".
The zone extends around 2km north to south and 1.5km east to west. However, drivers have vented their anger on internet message boards. "30km/h on the quays? That's a joke," wrote one contributor to the boards.ie website.
"Does this mean that running will attract penalty points and a fine?" quipped another.
A third contributor wrote: "The way they've sneaked this out ... with little advance notice or advertising, makes it look like a set up to 'catch' as many as possible Monday morning."
The council said: "Motorists can circumnavigate the zone by using the inner orbital route, which is signposted along the perimeter of the zone or travel through the zone at the appropriate speed."
It added: "The new speed limit will reduce speeding between junctions and facilitate smoother traffic flow.
"It will also promote modal shift to walking and cycling."