He escaped with a badly broken leg and lacerations to one foot.
"But he could have been killed. Thank God he wasn't."
Mr and Mrs Ngawhika believe that speed was the cause of the accident, and fear that next time the outcome could be much worse.
Neighbour Kathleen O'Hare, who has long regarded the open road speed limit as dangerous, last year gathered about 400 signatures on a petition to lower it. Billy's accident had reignited interest in the petition, she said, with more people signing it.
Mrs O'Hare and other residents have sought a meeting with Te Tai Tokerau MP Kelvin Davis to discuss their concerns.
"What we have essentially is a motorway running through the residential area of Kareponia, which includes a church, a marae, a kohanga reo, school bus stops and lots of tamariki," Mrs O'Hare said.
"People have expressed concern about the speed limit over the years but nothing has changed. No child would ever be exposed to this level of danger on Auckland's Southern Motorway, for example — why is it acceptable for our kids to have to live with this level of danger in their own backyard?"
She believed that reducing the speed limit was the only way to prevent a fatality.
"We had a situation last year where a driver was travelling at speed swerved to avoid something on the road and rolled his ute, ending up in the ditch," she said.
"The place where the car landed was 50m from where our tamariki catch the school bus. In different circumstances we would have been looking at multiple tangi."
Mr Ngawhika wrote to the predecessor of NZTA 20 years ago warning of the dangerous speed limit, and could cite examples of accidents that had occurred there over the years as a result of excessive speed.
"The speed limit on Kareponia Hill needs to be lowered now."