To the astonishment of colleagues and eyewitnesses, Mr Greig escaped with only minor injuries in the crash that knocked the motorway system out of action for nine hours near Auckland's Spaghetti Junction.
Speaking from Auckland City Hospital, Mr Greig said "airbags played a big part" in how he escaped without serious injuries.
The Cambridge man was still trying to piece together what happened.
"I don't know a lot myself now," he said.
He was in too much pain to talk about the incident further last night, said his partner Angela Rotherham, who travelled from Wellington to be by his side yesterday.
Eyewitness Gareth Thorne was on his way to work on the North Shore when he saw the truck plunged some 7m down the bank about 5.15am.
"It was frightening. It happened right in front of me," Mr Thorne said. "It reminded me of the Terminator movies -- how the big truck comes crashing down."
He was astonished Mr Greig wasn't killed. "I'm so surprised the guy survived. He is so lucky."
The eyewitness himself was also lucky. "If I had left 30 seconds later, the truck would've come down straight on top of my car and I would've been a goner."
The impact was so intense, part of the road was gouged out and had to be re-sealed.
Mr Thorne tried to alert other motorists to the danger. He quickly pulled over, reversed, put his hazard lights on, then beeped his horn to alert approaching traffic.
He called police and approached the truck, fearing the worst.
"I thought he was dead. I thought I was going to see something pretty horrific."
He saw a "tiny bit of movement" in the cab and then, within seconds, an ambulance arrived "just by absolute chance".
Yet Mr Thorne said the scene remained dangerous as cars approached around the corner at speed. It was also too dark to clearly make out the fertiliser, diesel and debris scattered on the road.
The cab was mangled and smashed into the road, with the windscreen wrecked. The second of two trailers stuck out at a 45 degree angle, while the first trailer was disjointed.
Mr Thorne said four fire engines, three more ambulances and a large group of police soon arrived.
Emergency services wandered up the bank, checking for any passengers who may have been thrown out the cab. Fortunately, Mr Greig was alone.
Mr Thorne said it was fortunate the crash happened at a relatively quiet time
"If it was a busy time, I'm sure people would have gone crashing straight into him, because the road was totally blocked and it was on a blind corner."
He still had trouble believing what he witnessed.
"It was amazing to see. I certainly won't forget it any time soon," he said. "It was unbelievable. He was flying off that motorway."
A nine-hour clean-up followed the crash as authorities removed diesel and the truck's powder fertiliser cargo.
Lanes on the Southern Motorway -- as well as the link road below, between the port and the Northern and Northwestern motorways -- were closed as emergency services worked to investigate the crash and clear the wreckage, causing delays into the afternoon.
Colleagues of Mr Greig, who had been driving for Regal Haulage for a decade, were amazed at the truckie's escape.
Regal Haulage driver manager Alan Pye said Mr Greig had been able to climb out of the cab himself after the crash, but was kept in hospital overnight for observation and an MRI scan.
"He is in a little bit of pain. They think he might have a cracked vertebrae, but they're not 100 per cent sure, which may have been a result of the seatbelt," Mr Pye said.
Mr Greig had only been driving for two hours yesterday, and had stopped for a rest break shortly before the crash, Mr Pye said. The company would investigate what caused the crash.
"We're just thankful that he's relatively unscathed, and we're more thankful that nobody else was injured -- that's a big thing for us," he said.
"The hero in this story is the truck, that he was able to survive the impact and a fall like that."
Regal Haulage director Brett McHardie also credited the Volvo truck's safety features for the driver's amazing escape.
But he added Mr Greig was "a very experienced driver" familiar with the Hamilton to Northland route.
"It's a great result for what could've been a horrible situation," he said. "He's doing really well."
Another colleague said Mr Greig was "a lucky boy".
Sergeant Jeff Gerbich of Auckland motorway police echoed the sentiment. "There was quite major damage to the truck," he said. "It was a very lucky escape."
The serious crash unit was still investigating the incident last night, police said, and it was too early to say how the crash happened.
- Additional reporting: Patrice Dougan
By John Weekes of NZME. News Service
