The American driver of a van which crashed near Turangi, killing three students, had told his passengers to put their seatbelts on, a coroner found.
But at the time of the crash on May 12 last year, four passengers had unfastened their belts and were thrown from the car.
Boston University students Ross Nicholas Jauberty, Austin Perry Brashears, both 21, and Daniela Rosanna Lekhno, 20, died at the scene.
Coroner Wallace Bain found the students could have survived if they had been wearing seatbelts.
They were among 16 international students who travelled from Auckland to Taupo on May 11, 2012, on a trip to walk the Tongariro Crossing, the coroner's finding said.