Police believe an ACT-registered Ford Falcon station wagon driving on the wrong side of the Federal Highway may have triggered a fatal crash about nine kilometres north of the ACT border.
The incident occurred about 7.30am and closed both sides of the Federal Highway for around seven hours.
The Falcon, a utility and a B-double truck were involved.
The driver of the Falcon wagon, a 28-year-old man, believed to be travelling south in a northbound lane of the highway, died at the scene.
Initial police investigations indicated the driver of the Mercedes B-double truck heading north had hit the Falcon and then veered across the median, with a utility on the same side of the highway caught up in the incident.
The crash triggered massive traffic congestion on the highway, with tailbacks of hundreds of vehicles in both directions.
NSW police, fire and rescue and ambulance all attended the scene.
The drivers of the truck and utility were uninjured and are assisting police with inquiries.
The 24-year-old truck driver was also been taken to Queanbeyan Hospital to undergo mandatory testing.
Heavy vehicles and buses were unable to be backed up on the highway and had to remain until the highway was opened in a limited way some hours later.
The two cars involved were removed by about 2pm, with the truck extracted a short time later.
Northbound traffic on the Federal Highway was diverted at Eaglehawk and southbound vehicles were being sent via Bungendore Road and the Kings Highway to the ACT until the road could be fully cleared.
A report is being prepared for the coroner and anyone with information or dashcam footage is urged to contact Monaro police, or Crime Stoppers on 1800 333 000.
