"I just saw his legs and one leg moved over to the other side and I thought 'He is alive". That was my worry," she said.
Her husband, Colin Kennedy, said cars often crossed the centre line and travelled too fast on the section of the road where the accident occurred.
The police said inquiries are ongoing.
In a statement, a NZ Post spokeswoman said it could not comment as there were ongoing investigations into the incident, "other than to say that our priority, and our thoughts, are with the NZ Post person, and supporting them and their family".
Figures released to the Herald under the Official Information Act show that of the 156 injuries since mid-2016 involving Paxsters, only two of the injuries were considered as being serious and needed professional medical treatment. The drivers were injured when the Paxsters collided with other motor vehicles.
The delivery buggies crashed 249 times during 2018, with the electric golf carts hitting vehicles, banging into fences or road signs and injuring posties.
NZ Post told the i this month the severity of the injuries are much less than those sustained on a bicycle based on its declining injury costs, and the increase in crashes is due to more Paxsters being in use.