Brett Andrew Button, 60, was sentenced to 32 years behind bars for killing 10 passengers and injuring 25 who had been celebrating a young couple's wedding in the NSW Hunter Valley.
He sped up while approaching a roundabout before losing control of the bus, which slammed into a guard rail and rolled onto its side.
Button was found to be driving while impaired by an opioid painkiller at the time, which he has denied in his recently lodged appeal against his "manifestly excessive" sentence.
The families of victims, first responders and insurance companies have since launched a class action to seek damages from Transport for NSW for physical and psychological injuries caused by the crash.
They claim the transport authority was responsible for alleged safety failings on Wine Country Drive at Greta, where Button was driving when the bus carrying 35 wedding guests crashed about 11.30pm on June 11, 2023.
On Friday, leave was granted for the statement of claim to encompass Acciona Infrastructure Projects Australia and Aecom Cost Consulting as co-defendants accused of negligence.
The companies are alleged to have been involved in the design and construction of the Greta interchange and its certification as compliant with regulations and suitable for use.
The application was unsuccessfully opposed by Acciona's solicitor Benjamin Goodyear, who noted that QBE Insurance has already started paying out claims related to the fatal crash.
The lawsuit might drag on for years, cost millions of dollars and at the end there might be no one with a damages claim who hasn't already been compensated by the statutory motor vehicle accident scheme, he said.
"(My client has) concerns that we may be embarking on an odyssey of litigation that may prove futile," Mr Goodyear said.
But Michael Gillis, acting for the class action, said the claims from the insurance company were different to claims for damages, which may be higher and can be paid out at a single time.
There are also people attached to the class action group who hadn't advanced claims with the insurance company, he told the court.
Justice Peter Garling said he understood Acciona didn't want to be a party to the litigation but it was already involved and becoming a defendant wouldn't exacerbate the cost.
Court documents claim the Greta interchange had numerous design flaws including being elliptical instead of round, using guard rails instead of run-off areas and having a gutter that was a "tripping risk" for larger vehicles.
The speed limit through the roundabout was also allegedly too high.
Audits by Transport for NSW were "inadequate to identify the unsafe design and construction of the interchange," the statement of claim said.
The matter will return to court in September.
Lifeline 13 11 14
beyondblue 1300 22 4636
