An inquest in Caernarfon on Wednesday revealed the young driver, 18-year-old Hugo Morris, had passed his driving test just over six months before he lost control of his car and rolled into a ditch on the way to a camping trip in Snowdonia.
He and his three friends Jevon Hirst, 16, Harvey Owen, 17, and Wilf Fitchett, 17, all from Shropshire, were killed after drowning in the ditch off the A4085 in Garreg, Llanfrothen, which had flooded due to heavy rain.
Senior coroner for north west Wales, Kate Robertson, announced she would write to the Department for Transport and the DVLA to express her concerns that fatalities could continue unless restrictions are placed on newly qualified drivers carrying passengers.
She also criticised the signage in the area, noting it did not provide adequate warning of the approaching bend.
Wilf's mother Heather Sanderson said: "We gave Wilf permission to go because we believed that the driver had passed his driving test, which he had, and we were more than happy.
"We had done our research and I think we would make the decision again, not knowing the outcome. I don't think our decision was flawed."
Dr Anton van Dellen, representing Harvey Owen's family, urged the coroner to consider a report for the prevention of future deaths.
He said: "One of the features of this case is that there were three children travelling with the driver on a road in North Wales, presumably heading to a place of recreation.
"That's a scenario which in my opinion is very likely to reoccur in the future."
Harvey's mother, Crystal, has been an advocate for graduated driving licences for new drivers. Speaking after the inquiry on Wednesday, she said she believed her child and his three friends were killed by an "outdated driving licence system".
The court heard additional signage and chevrons were installed after the collision. However, a broken fence, damaged in an earlier crash, remained unrepaired on non-council-owned land. The coroner announced plans to issue a report calling for a safety barrier and requested Gwynedd Council identify the landowner.
The friends were reported missing on 20 November, and their bodies were discovered the next morning by recycling collector Sion Griffith and his colleague, who spotted the overturned vehicle in a ditch.
Post-mortem results indicated that none of the teenagers suffered significant injuries, but their lungs showed signs of drowning. Forensic collision investigator Ian Thompson concluded that while the road's speed limit was 60mph, the critical speed for the bend was 38mph.
"The vehicle has come into the bend a little bit too quickly and has understeered," he said, adding that heavy rain had elevated water levels in a nearby river and the roadside ditch.
Thompson estimated the crash occurred shortly after 11.40am on 19 November.
"Mr Morris negotiated the right-hand bend, entered onto the grass verge, went down a steep embankment, and then into a water-filled drainage ditch," he said.