A man in his 40s was killed after being struck by a car at junction 16 on the southbound carriageway on the M1, near Dundalk at 2.45am on Sunday.
The road has since been closed for a technical examination, and local diversions are in place, while four people were also treated for non-life threatening injuries following this incident.
Gardaí have asked for any witnesses, especially road users who travelled along the M1 between the hours of 2.30am and 3am, to contact Dundalk Garda Station on 042 938 8400, the Garda Confidential Line on 1800 666 111 or any garda station.
Anyone with dashcam footage have also been encouraged to get in touch.
Elsewhere, a teenager sadly died following a road collision near Listowel, co Kerry on Saturday night. The boy was taken to Kerry University Hospital, but later died. The incident took place along the R555 at Duagh village, Listowel.
The driver of the car, and three other passengers were fortunately unharmed.
Anybody who was travelling on the R555 last night between 9.30pm and 10pm, and who may have video footage, has been asked to contact Listowel Garda Station on 068 50820, the Garda Confidential Line on 1800 666 111 or any garda station.
A man aged in his 20s also died while driving on Skrine Hill, Roscommon, after his car was overturned, early on Sunday morning. No other vehicles were involved, according to Gardaí.
Local diversions have been put in place, while the road is closed. Anybody who was travelling in the area between 2.30am and 3am, and who has camera footage (incl dashcam), has been urged to to contact Roscommon Garda Station on 090 663 8300, the Garda Confidential Line on 1800 666 111 or any garda station.
A man in his 40s also died in Donegal, following a motorcycle crash on the R262 near Glenties shortly before 4pm yesterday. The motorcyclist was pronounced dead a short time later, with that section of road between Kilraine and Frosses closed off for forensic examination.
Gardaí in Glenties are urged to contact them on 074 9167100.
These deaths which occurred on Irish Road Safety Week, bring the number of people who have died on Irish roads this year, to 144.
