A motorcyclist who crashed in June last year, killing himself and a teenage passenger was nearly five times over the limit and speeding, a coroner has found.
Dee McMahon, 49, and Natalia Austin, 18, died after Mr McMahon's Harley-Davidson hit the median barrier near the Terrace Tunnel in Wellington on June 28.
A report by coroner Christopher Devonport said Mr McMahon was nearly five times over the legal alcohol limit and was travelling at speeds of up to 140km/h at the time of the fatal crash.
Mr McMahon's partner, Monique Elston, recalled sharing at least a quarter of a bottle of bourbon and some cans of bourbon and coke with him at a party the day before.
She told police Mr McMahon may also have drunk some wine.
In the inquest into his and Ms Austin's deaths it was revealed Mr McMahon drunk between 22 and 42 standard drinks the day before the crash, putting him nearly five times over the legal alcohol limit at the time it happened.
A toxicology report found Mr McMahon also had a cocktail of prescription drugs, including morphine and tramadol, in his system at the time of his death, neither of which should have been mixed with alcohol.
Mr McMahon required pain medication following a previous motorcycle accident in 2011 where he was hit by a car while riding.
Mr McMahon was the partner of Ms Austin's boyfriend's mother and had been taking the Featherston teenager for a spin on his motorbike when he lost control about 400m north of the Terrace Tunnel and hit the median barrier.
One witness guessed she saw the bike hit the barrier about ten times, and each time "bits of the bike were flying off".
Mr McMahon and Ms Austin died at the scene after being flung from the bike on to the motorway.
Ms Austin's father, Tony Austin, told Fairfax the coroner's findings had worsened his family's grief.
"You let your little girl go and you hope she's going to be looked after by adults. She trusted them, and they've let her down miserably."
He said he hoped the findings might save someone else's life.
"If anything's to come out of this it's that, just because people are adults and parents and homeowners, it doesn't mean you can trust them completely. "You've got to use your own judgment as a teenager.
"Just be vigilant, and trust your instincts, and if it doesn't feel right, don't get in that car or on that bike.
"Even if you think it may seem disrespectful, if you think they've been drinking or whatever, say no."