The ACT Supreme Court heard the 15-year-old boy had been running across Clift Crescent in Richardson on March 27, 2009, when he was hit by the woman's car.

The driver had been distracted by two other boys, a cousin and friend of the 15-year-old, who had just emerged from the bushes and sprinted across the street, the court heard.

The driver told the court she slowed down. The boys were looking back and she believed they were going to run back across the road.

But then she saw a third boy ran out from behind the path.

He looked left, the court heard, and the woman hoped he would look right and see her but he did not.

"I like kept slowing down and then I thought he was going to stop and so I just went normal and then he hit me so I braked," she told the court.

The teenager had no memory of the accident.

The 15-year-old suffered catastrophic injuries in the accident, Justice Michael Elkaim said in an 18-page judgement published Thursday.

But the judge found that even if the woman had breached her duty of care to the boy, he had been unable to prove she caused his injuries.

A registered nurse told the court he needed two people to lift him.

She said his funding "sharply decreased" when the National Disability Insurance Scheme took over.

"Plainly, the grand intentions of the scheme have not translated to the plaintiff’s benefit," the judge noted.

He has had to have less speech therapy and other services have either been curtailed or diminished.

The judge saw for himself when he heard oral evidence from the man at the home in Sydney.

He said the man's life had been "completely overwhelmed" by his injuries.

"The sense of humour that he maintains is the only element of a ‘normal existence’ that can be identified," the judge said.

The man was significantly cognitively impaired.

When not in bed he was restricted to a wheelchair and his legs bound to it.

In bed he needed to be moved by two people.

There was little prospect of improvement other than help from physiotherapy and speech therapy, the judge said, and the man had lost a good deal of his life expectancy.

"His remaining 33 years will be plagued by the disability which he now suffers," he said.

But the judge found the plaintiff, who had the onus of proving causation, had failed to establish that the woman's negligence caused his injuries.

He pointed to the impossiblity of knowing which path the boy had taken, and that though the woman had taken a risk in assuming he would see her, the accident was already unavoidable.

"Accordingly, even if there was a breach of duty of care on the part of the defendant, the plaintiff has not established liability because he has not proved that any breach caused his injuries," he said.

The judge said, in the judgement published Thursday, that had he found for the plaintiff he would have awarded more than $8.8 million in damages.

But that amount would have been reduced by 75 per cent, which the judge found was the extent of the boy's contributory negligence.

The plaintiff was ordered to pay the driver's costs of the case.