A young woman has died in hospital days after a fiery South Coast crash that killed both of her parents and left her sister critically injured.
Annabelle Falkholt, 21, was airlifted to Liverpool Hospital on Boxing Day after her family's car was hit head-on at the Princes Highway near Ulladulla.
NSW Police said she passed away at the hospital on Friday.
Her sister Jessica Falkholt, 28, continues to fight for life after she was pulled from her parents' car before it burst into flames.
She remained in a critical condition at St George Hospital on Friday afternoon.
Lars Falkholt, 69, and his wife Vivian, 60, died instantly when their car was hit by a four-wheel-drive that veered onto the wrong side of the road at about 10.45am.
Craig Anthony Whitall, 51, who was behind the wheel of the Toyota Prado, also died on impact.
Annabelle and Jessica were pulled from their car by bystanders and taken to hospital, where they were surrounded by family and friends in intensive care.
The Falkholts were travelling back to Sydney after a short Christmas break when they came into the path of Mr Whittall, who was on his way home from a methadone clinic.
Mr Whitall, who was known to police, was making the hour-long drive home to Ulladulla after visiting the clinic in Nowra on Boxing Day morning.
About 50 kilometres into the 65-kilometre trip, as he neared the Bendalong turnoff, his four-wheel-drive failed to negotiate a sweeping left-hand bend and crashed into the Falkholts' Mazda.
Crash investigators are examining the cause of the accident and whether methadone played a part.
Mr Whitall's son told Seven News his father had been his "hero" and his "idol".
NSW Police urged drivers to slow down and take care on the roads, with Ms Falkholt's death bringing the NSW holiday road toll to 23.
A man who crashed his motorbike into a sign near Queanbeyan on Thursday night was the 22nd person to die on the state's roads since December 15.
Assistant Commissioner Michael Corboy from the Traffic and Highway Patrol Command, said there had been "too many" crashes this year.
"We are urging drivers to take responsibility for their actions and to slow down to ensure no more lives are lost this year," Assistant Commissioner Corboy said.
The state's premier, Gladys Berejiklian, said the deaths were "tragic".
"To lose anybody [at] any time is tragic, but especially at this time of year," she said. "My heart breaks every time I've heard of those tragic circumstances."
Ms Berejiklian said drivers must take responsibility for driving safely.
"No matter what rules are in place, when people do the wrong thing it has tragic consequences," she said. "We cannot get away from the fact that people need to obey the laws that are in place."
Operation Safe Arrival, the annual NSW Police road safety campaign, will continue until 11.59pm on January 1.