Henryk Konopacki died instantly in the horror smash near Barham in May, but expert accident investigators could find no reason why he veered off the London-bound carriageway.
The 57-year-old Polish driver was said to be very experienced and carrying a load of potatoes at the time of the crash, which closed the road for several hours.
Wreckage of the red lorry that hit a bridge on the A2, killing Polish driver Henryk Konopacki Picture: Bun Johnson
A post mortem examination revealed he suffered multiple injuries and had a high level of alcohol in his liver.
But a pathologist's report to the hearing said the results could not be used to conclude he had been drinking before the crash.
The incident was witnessed by taxi driver Ben Brazil and his passenger Anthony Stigle, who were behind the truck on the A2 in the inside lane.
Mr Brazil said: "The traffic was very light and the lorry was doing about 55mph. I was about three car lengths behind when I saw the lorry weave a bit then go straight off to the left into the bridge. There were no brake lights.
"I knew from the moment it started wavering there was going to be an accident."
Wreckage of the red lorry that hit a bridge on the A2
Mr Stigle added: "I thought 'he's going to hit the bridge'. It was like it was on rails because it was on the crash barrier. I said, 'that will be a fatal'."
Police forensic accident investigator Robert Giles told the inquest he could find no defects with the road or vehicle - or adverse weather conditions - that might have contributed to the accident.
He said the lorry had mounted the crash barrier near the bridge and the cab had been destroyed in the impact.
A study of the lorry's tachograph card revealed the driver had been taking adequate rest periods and investigations showed he was not using his mobile phone at the time.
"There is no obvious reason why the vehicle left the road," he said.
Emergency services at the scene of the fatal crash on the A2 near Barham
Mr Konopacki's daughter, Ann Cedrowski, told coroner Rebecca Cobb her father was on medication for hypertension, but had never suffered from any episodes of blacking out.
She also said he was in good spirits and looking forward to coming home for a family celebration.
Recording that his death had been an accident, Miss Cobb said: "For reasons not established by the evidence, his truck left the road.
"There is no evidence of contributory factors, defects to the vehicle or road, or suicidal intent."