Cellphone usage and lack of a seatbelt are being scrutinised by police investigating Saturday's Te Puna crash which killed 26-year-old Bay mother Tracey O'Brien.
The head of Western Bay road policing, Senior Sergeant Ian Campion, said the preliminary crash report indicated weather, speed, alcohol and road conditions were not contributing factors, and the investigation now centred around two main issues.
"We believe Ms O'Brien was manipulating her cellphone while driving and also believe she was not wearing her seat belt. The preliminary indications are these factors contributed to the crash."
Mr Campion said he was "absolutely gutted" at the number of fatal road crashes this year.
He said there had been six fatal crashes on Western Bay roads this year, the same number for the whole of last year. Apart from one, which involved a medical condition, every one of the other 11 crashes were "absolutely preventable".