Parnell had dozens of broken bones, is confined to a wheelchair, and needs more surgery. "I lost basically everything in one minute," he told the Herald on Sunday.
Parnell said he wanted to apologise to the families of the dead and injured.
"I am so sorry to all the families involved," he said.
"It is something I would never wish upon anyone's families. Those two shouldn't have died that day. I think about it every day."
However, he said there were still questions about the actions of two other drivers. He hired a private investigator who found two cars had come "out of nowhere" to stop in front of Parnell.
"I would like them to step up and be made accountable for their part in the accident."
Parnell said he was teaming up with professional drag racers to educate boy racers.
"I just feel like I need to do the most and best I can to make this never happen again."
Normanby Fibreglass owner Paul Schrader, who tried with his forklift to rescue a motorcyclist pinned beneath the van, said Parnell had made a bad decision.
"He crossed the white line and went straight into the path of the motorcyclists."
He said plans had recently been drawn up to change the intersection and add a right-turning bay.
