A motorist was slammed with thousands of dollars in fines and stripped of driving privileges after he was clocked at almost 190kmh by Riverina Highway Patrol on the first day of the double demerits period.

Police say the Toyota sedan was spotted on the Burley Griffin Way at Moombooldool, west of Ardlethan, around 3.30pm on Thursday and it reached a top speed of 187km along the 100kmh road.

"Officers stopped the car and issued the driver, a 28-year-old man, with traffic infringement notice which carries a fine of $2794 and the loss of 12 demerit points," police said.

The man's licence was also suspended.

Police are investigating the deaths of a man at Booligal, in the region's west, on Good Friday and a motorcyclist who collided with a B-double on the Snowy Mountains Highway on Easter Saturday.

Bystanders, police and paramedics worked in vain to save the life of a 54-year-old man who flipped an ATV on Boxyards Road, just north of Booligal, around 8pm on Friday.

Initial inquiries indicate the man was westbound when he swerved to avoid a kangaroo, causing the vehicle to roll, police said.

Despite CPR efforts by witnesses and police, who worked until paramedics arrived and took over, he died at the scene.

Murrumbidgee Police Dstrict officers called for further witnesses or anyone with information to come forward as they prepare a report for the coroner.

The Snowy Mountains Highway was closed for much of Saturday in the wake of a crash near Kiandra, south of Tumut, on Saturday morning.

The highway was closed in both direction between Link Road and the Providence Portal park entry for nine hours after tragedy struck when a motorcyclist collided with a B-double around 11.15am.

The rider, a man, had succumbed to his injuries by the time Monaro Police District officers arrived at the crash site.

The man who had been behind the wheel of the truck was taken to Cooma Hospital for mandatory testing following the crash, police said.

It took some hours for the wreckage to be cleared and the scene examined, with the highway reopening completely around 8pm.

The 2024 Easter operation continues until the end of the double demerit period, which winds up at 11.59pm on Monday.