Update 9.18pm: A car travelling at 144km/h in a 100km zone was the biggest speeding culprit on National Slow Down Day.
The Garda initiative started this morning, with extra checkpoints in place around the country until 7am tomorrow.
The message is for drivers to reduce their speed, which is a factor in a third of road deaths.
Last year saw a record low number of fatalities on the roads.
But Derek Cloughley from the Gardaí's road policing department says they cannot be complacent.
He said: "157 tragically lost their lives on Irish roads last year. It is the lowest in terms of road safety but there is absolutely nothing that we can do to be complacent about that.
Update 5.21pm: Gardaí stop over 10,000 motorists as part of National Slow Down Day
Motorists are being urged to reduce speed to save lives on the roads.
A Garda crackdown is underway with extra checkpoints in place across the country.
National Slow Down Day has seen over 10,000 people stopped already with some vehicles in Dublin, Kerry and Monaghan found to be breaking the speed limit by up to 40 kilometres an hour.
Derek Cloughley from the Gardaí's Road Policing Bureau says they are putting lives in danger.
He said: "By keeping to the speed limit, people will have no issue today or any other day.
"When people travel in excess they are putting their life and other people's lives in danger.
"In terms of road safety, it is going to make it a much easier and much safer journey for you."
Notable Incidents include:
70km/h in a 50km/h Zone on the R445, Ballymany, Newbridge, Kildare
78km/h in a 60km/h Zone on the R563, Faha, East Faha, Kerry
139km/h in a 120km/h Zone on the M7, Ballyadding, Ballybrittas, Laois
135km/h in a 120km/h Zone on the M9, Danesfort, Kilkenny
109km/h in a 100km/h Zone on the N25, Loughaderry, Midleton, Cork
93km/h in a 100km/h Zone on the N17, Falnasoogaun Or, Ropefield, Ballymote, Sligo
132km/h in a 100km/h Zone Minish, Killarney
144km/h in a 100km/h Zone N2, Monaghan
140km/h in a 100km/h Zone N2, Monaghan
Earlier: Gardaí stop 9,000 vehicles as part of #NationalSlowDownDay
Over 9,000 vehicles have been stopped today as part of a Garda crackdown on speeding - with 26 found to be breaking the limit.
National Slow Down Day is a 24-hour Garda initiative which aims to reduce the number of deaths on our roads by encouraging drivers to reduce their speed.
#SlowDownDay began 7:00am this morning. An Garda Síochána & GoSafe checked speeds of 2,300 vehicles. 4 vehicles detected travelling in excess of the speed limit (7:00am-8:30am) including 70 km/h in 50km/h zone on R445, Newbridge. Gardaí remind road users to #SlowDown Speed Kills! pic.twitter.com/kkYXE9rdaN— An Garda Síochána (@GardaTraffic) May 25, 2018
Derek Cloughley from the Gardaí's Road Policing Bureau has details of some of the cars they have stopped so far.
"The first one was on the N2 in Monaghan where the driver was doing 144km/h in a 100km/h Zone, the second one was on the Stillorgan Road in Dublin where a driver travelling at a speed of 105km/h in a 60km/h Zone," said Mr Cloughley.
"Our intention now is to have zero detections. That's what this initiative is about.
"We're asking people to stick strictly to the speed limit and then they'll have no problems in relation to penalty points or fines."