Two people died instantly after their car went out of control and struck a tree at around 11pm on Sunday, bringing the weekend's death toll in the Republic to six.
The incident occurred at Kilcarry, near Clonegal, Co Carlow.
The driver, a 23-year-old man and the passenger, an 18-year- old woman, were pronounced dead at the scene. There were no other occupants and no other vehicle was involved.
Their names were being withheld by the Garda until relatives had been informed.
The deaths brought to 216 the number of people killed on the Republic's roads to date this year, which compares with 251 at the same time in 2006.
A total of 16 people have been killed on the roads this month, compared with 17 for all of August last year.
The fatalities in Carlow on Sunday followed the deaths of four other people in road crashes at the weekend.
A 21-year-old motorcyclist died at 4am on Sunday in the Sandyford Industrial Estate near Leopardstown in south Co Dublin after losing control of his bike on Burton Hall Road. The man was pronounced dead on arrival at hospital.
Three men died on Saturday in separate collisions. James McMahon (44) from Assumption Park, Roscrea, died at 10.55pm when he was knocked down while walking on the N7 outside Roscrea.
Also on Saturday night, a man in his forties died in a collision on the N3 near Navan. He was the front seat passenger in a car that collided with another vehicle at 8.55pm.
Another man, 64-year old Patrick Phelan died when his car collided with a truck on the M7 near Monasterevin, Co Kildare.
His female passenger survived and was brought to the Midlands General Hospital in Portlaoise, where she is in a critical condition.
In the North, a 21-year-old man was arrested after a two-car collision on the M1 sliproad, near Lisburn.
Police have said there were no fatalities. Four passengers of one of the cars, three women and one man, remain in hospital. The man is in a critical condition in intensive care.
The 21-year-old was charged with two counts of causing death or grievous bodily harm and one count of driving with excess alcohol.