A 39-year-old man was being held for questioning at Portlaoise Garda station last night in connection with a fatal road crash in which a passenger died yesterday morning.
The incident happened at about 7.05am as the busy morning rush was getting under way.
The man who died was a passenger in a van that was involved in a collision with a lorry at Clonad on the N8, between Portlaoise and Abbeyleix. His body was removed to the Midlands Regional Hospital in Portlaoise for a postmortem.
The lorry driver was treated for shock at the scene.
The other driver was taken by ambulance to the Portlaoise hospital to have his injuries treated.
A spokeswoman for the hospital described the injured man's condition as "comfortable" yesterday.
The section of the N8 between Portlaoise and Abbeyleix was immediately closed for technical examination after the collision.
Diversions were in place yesterday morning and many motorists experienced long delays as a result.
AA Roadwatch advised motorists to postpone travelling in the area if at all possible. The road reopened just before 3.30pm.
At noon, gardaí arrested a man in connection with the fatality. He was taken to Portlaoise Garda station and detained under Section 4 of the Criminal Justice Act.
The Act allows for his detention until noon today, by which time he must be either charged or released.
The chief executive of the Road Safety Authority, Noel Brett, expressed his condolences to the dead man's family yesterday.
"Our thoughts go out to the families of those people whose lives have been shattered in a split second," Mr Brett said.
He added that, despite regular reports of road fatalities, the message about road safety was clearly getting through.
Mr Brett said many drivers were now taking pride in how they used the road.
"2006 had the second-lowest number of road deaths in over 41 years," he said.
Up to 9am yesterday, 31 fewer people had been killed on the roads compared to the same period last year, Mr Brett added.
Of those 229 deaths, 92 were drivers, 52 were pedestrians and 50 were passengers.
Motorcyclists accounted for 23 deaths.