Two men and two women were killed in crashes on roads around the country and four people were injured over the weekend. A 26-year-old man was killed and another young man critically injured in a two-car collision in Co Limerick yesterday.
Three other people including a nine-year-old child were rushed to hospital following the fatal crash.
The collision happened at 9.15am on a straight stretch of road at Uregare, Killmallock, Co Limerick, where both vehicles were travelling in opposite directions.
The deceased was driving in the direction of Kilmallock when his car was involved in a collision with another vehicle travelling in the opposite direction towards Bruff.
Gardaí and the ambulance service were called to the scene but the man was pronounced dead before being brought to the Mid-Western Regional Hospital.
The victim of the accident was named last night as John Buckley from Kilfinnan, Co Limerick.
The 21-year-old male driver of the second car was last night being treated at the intensive care unit of the hospital. His condition has been described as critical.
A nine-year-old girl, a woman and a third man, who were all passengers in the first vehicle were also treated for injuries, which were described as not life-threatening.
A full technical examination was carried out yesterday at the scene and an officer from the Accident Investigations Specialist Unit in Tralee was called to Co Limerick to help determine how the crash happened.
In Cavan, a 17-year-old man was killed when the car he was driving collided with a truck on a minor road.
Patrick Cox, Cornea, Arva, Co Cavan, died at Crossdoney, Arva, shortly before 9pm on Saturday.
Mr Cox was alone in the car at the time of the crash and the truck driver was not injured. The scene was preserved for technical examination.
Gardaí in Cavan are investigating the incident and have appealed for witnesses.
The weekend's fatalities bring to 354 the number of people killed on roads in the Republic so far this year.
Meanwhile, in Northern Ireland, two young women have died and a man is in a critical condition in hospital after road traffic crashes at the weekend.
The two women, both from Rasharkin, Co Antrim, died in a collision in the county.
Claire Wakeland (23) and Lisa McFarland (25) were reported to have been on their way home in the early hours of Saturday when the car they were travelling in stopped at the side of Ballybogey Road in Portrush and they got out.
What happened next is unclear but within a short time three cars were in collision and the two women, one of them a mother of two young girls, were dead.
Four others understood to have been involved in the collision are not thought to be injured.
The injured man was hit by a vehicle at Shore Road, Bally-ronan, near Magherafelt, Co Derry, on Saturday at about 6pm. The PSNI said he was a pedestrian and they believe just one vehicle was involved.
The driver did not stop after hitting the man and the PSNI has appealed for him to come forward.
They have also appealed for anyone who might have witnessed the crash to contact them.
So far this year, 120 people have died on Northern Ireland's roads.