It began at 7 am and runs through to 7 tomorrow morning.
There'll be a more visible garda presence on roads across the country as they remind drivers of the dangers of speeding.
It comes after a continued increase in road deaths, with 127 people killed in road colisions so far this year.
Assistant Garda Commissioner for Roads Policing, Paula Hilman says August has been especially difficult.
'We've seen a really tragic month where a quarter of all road deaths have occurred within the month of August. Internally we send out operational orders for Slow Down day and when I signed that operational order on the 15th of August it said there had been 105 road deaths on Irish roads and today two weeks later it's 127 and I think you know, that that's really stark.'
