ROTORUA, New Zealand - Three university students killed near Rotorua, New Zealand, when their minivan rolled might have survived had they been wearing seat belts – sounds like a classic advertisement for buckling-up.Constable Tina Mitchell-Ellis told a coroner's court the three students from Boston in the US who died and a fourth who suffered brain trauma in the crash in May 2012 weren't wearing a belt and were thrown from the van. Four others who were belted suffered only minor injuries.The students were in New Zealand on a study-abroad programme and were driving to the start of a hike.ROLLED FOUR TIMESThe driver, Stephen Houseman, pleaded guilty at the time to careless driving and was disqualified from driving for six months.Mitchell-Ellis said Houseman had reminded the others to buckle-up. Later he became distracted and drove on to the side of the road before over-correcting. The van rolled four times.Houseman said: "As we were flipping, everyone was screaming but it was more like a roller-coaster scream. I just kept screaming 'I'm sorry. I'm sorry. I'm sorry.' I didn't know what else to say."Police said alcohol and drugs weren't involved and the debris indicated Houseman probably wasn't speeding when he crashed. Police said it was his first time driving in New Zealand and his first time driving a minivan.