The extra focus by police on ensuring seatbelts are used isn't having the desired effect, as more are caught out.

A driver was thrown from their car during a crash on Tram Road in Canterbury on Wednesday morning, and was not wearing a seatbelt.

"Seatbelts are there for a reason - to protect you," Senior Constable Tu Maaka, the officer who attended the crash, said.

"The person involved in this crash is very lucky it didn't turn out worse."

Police announced last week extra measures would be put in place, after the number of deaths of those who weren't buckled up had nearly doubled in the past two years.

Assistant Commissioner Dave Cliff said that was unacceptable.

"Almost a third of people who die on our roads are unrestrained vehicle occupants and these are all deaths which are entirely preventable," he said.

"We are at a loss to understand why there has been such a massive increase in people not wearing their seatbelts."

In 2016, the seatbelt wearing rate for drivers and adult front seat passengers was 96.5 per cent; a drop from the 97.1 per cent observed in 2014.

He said a seatbelt reduced the risk of death risk by 50 per cent for those in the front seats and by 75 per cent for back seat passengers.