Everything fell apart after Tristan Kennedy, 19, crashed his runaway trail bike into a semi-trailer in December 2007 and spent 19 months in hospital recovering from horrific injuries to his body and brain.
His mate, Dwayne Hodge, who was also on the bike, was killed.
Tristan's distraught father, Ashley, suffered a stroke and heart attacks soon after and was forced to give up his job as an interstate truck driver. The family was plunged into poverty.
One of Tristan's brothers ''went off the rails'' and got into trouble with the police. A sister, who lent the trail bike for the day, has continued to suffer.
The blended family - seven of the 10 children lived at home at the time - had to move house twice to be close to Tristan through his long stays in two hospitals. And his ebullient stepmother, Peta, who has raised him since he was 18 months, confessed she frequently had to ''hibernate'' in her room to maintain the strength needed to keep the family going.
''He's so different from what he was before,'' says Ashley. ''It's heartbreaking.''
A report by Access Economics estimates the financial cost of road accidents among the state's 15- to 24-year-old population was $1.5 billion in 2010. This includes the costs of medical care and social support, insurance, productivity losses, police and fire rescue, and vehicle related costs.
More than one young person a week - 73 in all - was killed last year in NSW and nearly 15,000 were injured.
But the hidden toll is among the 393 young people who acquired a permanent disability. This would have ''a substantial personal and economic impact on family and friends, and impose a large cost on healthcare and social support for the remainder of their lives,'' the report said.
The spotlight this week on the death of the actor Jon Blake at 52 was a reminder of what acquiring a ''permanent disability'' can mean. Blake, a rising screen star, was left with severe brain injuries after a car crash in 1986 at the age of 26, and required round-the-clock care until his death.
Road deaths have fallen dramatically as a result of seatbelt laws, drink-driving restrictions, stricter enforcement and cultural change. Between 1980 and 2010 the nation's annual road death rate declined from 22.3 to 6.1 deaths per 100,000 people.
But Nick Rushworth, the executive officer of Brain Injury Australia, says: ''Better designed vehicles and roads and better-quality trauma care mean people are surviving with much more severe injuries and disabilities than 15 to 20 years ago. And they need a much greater level of disability services and support.''
For the seriously injured survivors, some things have not changed.
This is what Tristan Kennedy has learnt. The silly decision he made as an impetuous schoolboy - to ride a trail bike illegally on a suburban street and not to wear a helmet - has reverberated for years through his life and the lives of many others. It has left the former rugby league player with impaired speech, memory and balance, and a spastic right arm still in a splint.
The truck driver, who saw the terrified faces of the two young men as they tore down a hill with the throttle jammed, could not work for a year after the accident.
Tristan's girlfriend, Samantha Robertson, has stuck by him but life is different from when he was outgoing and sporty. ''He will yell at us and then he will forget why but he doesn't understand why we don't forget.''
Tristan will address 12,000 high school students at the three-day Australian Youth and Road Trauma Forum from June 21 at the Acer Arena. His message will be short and simple: Don't be stupid; be responsible.
''I thought I was too cool to wear a helmet,'' he says, sitting in the family's home in Whalan, near Mount Druitt.
The forum, organised by Westmead Hospital trauma unit and The Balnaves Foundation, will present a simulated crash and aim to sensitise students as they enter their learner driver years.
Raphael Grzebieta, a professor of road safety at the Injury Risk Management Research Centre at the University of NSW, says Australia has come a long way. ''But speed is the last frontier. And in NSW we don't have anywhere near the number of covert speed cameras that are required.''
The Access report found young males were twice as likely to be seriously injured as other people, and that poor driving behaviour was the primary cause. Compared to people over 25, young drivers were more likely to use mobile phones, even to send or read text messages, use MP3 players, show road rage, drive under the influence of alcohol or drugs, and speed.
In some ways the Kennedys consider themselves lucky. Tristan did not get a $7.7 million payout like Jon Blake, who was not at fault. But the state's Lifetime Care and Support Scheme was implemented to cover all road crash victims, regardless of fault, just two months before Tristan's accident. It has paid for all his therapies and medical bills, and carers 12 hours a day.
If he had suffered similar injuries from any cause but a road crash, he would not be covered. That is why advocates are pushing for a national disability insurance scheme.
The Kennedys consider themselves lucky in another way, too. It only seemed that they might fall apart. ''We've been tried and tested,'' Peta says, ''but the family has held together.''