Glad I do not live - or work - in town...
To introduce it like a blanket limit is mental and they need their heads examined... fair enough for small residential streets etc... but major through-roads in and out of town should be at least 50kph (and many could be 60kph without any issue). Where is the proper rationale that adds up to back this disaster?
Traffic is already gridlocked / strangled and now they'll make it worse again. Probably one of the lads/lasses in the council has it as a KPI for his/her bonus to reduce accidents / or increase revenue-take on speeding fines... so rather than fix the roads or crazy traffic situations at some junctions etc... cheaper to do it this way for his/her budget. The fact that it will serious impact the local economy (shops / businesses around town and further skew the house prices) doesn't matter - only looking at the small picture not the overall impact. In the meanwhile the road surfaces are still poor, junction layouts dangerous, cycle lanes where there is no space to house them (so where is a car or truck supposed to drive if the lane is not wide enough).
Dublin needs a serious overhaul with regards transport policy... put in the long-talked-about metro line to the airport, put in another 1 or two metro lines to service commuters to get in and out of town without getting stuck in traffic (bus and Luas just as bad as a car as still sharing "surface space" with all other road users), clear major through roads such that they do not get gridlocked at junctions and up the speed limit on them while reduce speeds on minor roads. Yes this would cost, but it also puts money back into the economy (directly through the capital spend on such projects, but also indirectly through improved economic activity in town, enable commuting such that people don't need to live in or near town to get in to work which means equalize house prizes across the greater Dublin area... and more.
As usual they are quoting "Ireland way behind our neighbours" when talking about lowering speed limits... but all the other things like metro lines (in EVERY European capitol), public transport that runs (and doesn't strike) and is on time, Flexible speed limits (dependent on time of day or traffic density) really help to keep traffic optimised. We are doing none of that... it costs money and would take effort... let's just reduce the speed and nobody will notice the other problems.
Sure, maybe if they reduced the speed to 30kph across the island we'd be able to cut road deaths by 90%... The fact we would no longer be able to commute to and from work within a reasonable time, or get supplies around our island in an affordable way (time is money for haulage which just gets factored into our products at the till), or the huge negative impact on the environment through CO2 emissions as all cars use more fuel per km traveled at 30kph than 80kph...
rant over... sighhhhhh.