More than 194,089 vehicles have been checked for speeding as part of National Slow Down Day.
Gardaí said 255 of them were detected travelling in excess of the speed limit.
In one case, a vehicle was recorded 181km/h in a 120km/h zone on the M1 at Lusk, Co Dublin - 61km/h over the speed limit.
Another vehicle was detected travelling at 151km/h in a 100km/h zone on the N72 at Gort na gCros near Mallow, Co Cork.
The 24-hour operation runs from 7am today until 7am tomorrow, with more than 1,000 speed enforcement zones put in place across the country involving gardaí and GoSafe vans.
Drivers are being urged to check their speed and slow down.
Gardaí say speed is a contributory factor in about one third of fatal road traffic collisions.
Almost 96,000 vehicles were detected speeding in the first eight months of this year, according to gardaí, an increase of 15% on the same period last year.
One of the highest speeds detected recently was someone travelling 223km/h in a 100km/h zone in Co Donegal.
Chief Superintendent Paul Cleary of the Roads Policing Bureau said that in another case, a driver in Patrickswell, Co Limerick, was caught travelling at 192km/h in a 120km/h zone.
The man was charged with dangerous driving and convicted in court of careless driving.
In 2018, there were 142 road deaths, which is the lowest on record.
As of 16 October this year, there have been 117 road fatalities, an increase of five on this date last year.
Since 07:00, GoSafe has checked the speed of 138,171 vehicles with 219 vehicles detected travelling in excess of the applicable speed limit. . Notable speeds include: 138km/h in a 80km/h Zone, 84km/h in a 50km/h, 151km/h in a 100km/h Zone pic.twitter.com/SAShQv2T1c
— An Garda Síochána (@GardaTraffic) October 18, 2019
Chief Supt Cleary said that with the darker, wetter weather approaching, vulnerable road users, such as pedestrians, cyclists and motorcyclists, will be at higher risk over the coming months.
He called on people to reduce their speed - not only today, but every day.
Chief Executive of the Road Safety Authority Moyagh Murdock said that excessive and inappropriate speeding is the biggest killer behaviour on our road, and is a contributing factor in a third of all fatal crashes.
During last year's campaign, GoSafe checked the speed of 164,032 vehicles and 276 were detected travelling in excess of the applicable speed limit.
From 1 January to 31 August, there were 95,998 speeding detections, a 15% increase on the same period last year.
