In upholding a lower court decision on Thursday, Ontario's top court found no problems with what the trial judge had done.
"The key issues involved the standard of care to be observed by police officers and by a bus driver," the Appeal Court said in its judgment.
"The trial judge was uniquely positioned to decide whether he needed expert evidence to determine those standards of care and his rulings attract deference."
The case arose in December 2000, when Shaun Davis, 21, travelling from Calgary, boarded a Greyhound in Ignace, Ont., en route to a Christmas family gathering in Pictou, N.S.
Police in the hamlet investigated after Davis told the driver that some passengers had been going through his baggage and that people were after him or wanted to beat him up, court documents show.
However, he also said he did not want to see a doctor and just wanted to get home.
The officers concluded Davis, although anxious and mildly paranoid, had committed no crime, seemed calm, well-mannered, and rational. They allowed him to board after assuring driver Albert Dolph that he posed no threat.
About an hour later, Dolph asked Davis to leave the stairwell and return to his seat. Instead, Davis lunged at Dolph and grabbed the wheel, prompting the bus and its 32 passengers to veer off the road between Kenora and Thunder Bay and flip.
One person was killed. Many passengers were hurt.
Also named in the lawsuit were the two police officers as well as Davis himself.
After a 65-day trial that started in 2010 and heard from 83 witnesses, Superior Court Justice Terrence Platana dismissed the action against everyone except Davis.
In their appeal, the passengers argued Platana was wrong to exclude the expert evidence of a specialist in police training, who believed the officers should have noted Davis was delusional and stopped him from boarding.
They also maintained Dolph should have slowed down after observing Davis was agitated, and the judge was wrong to disallow another expert who wanted to testify to that effect.
The Appeal Court said Platana was right to exclude the "unnecessary" expert evidence.
"There has been growing recognition of the responsibility of the trial judge to exercise a more robust gatekeeper role in the admission of expert evidence...to ensure the evidence is genuinely necessary," the Appeal Court wrote.
The top court agreed with Platana that Dolph was not negligent, and had been driving reasonably before the crash.
"There was nothing Dolph knew or ought to have known that should have caused him to change the way he was driving the bus," the Appeal Court said.
Davis never defended against the lawsuit and was found liable by default.