"Those key decisions in the first four hours after injury are absolutely crucial," Dr Coleman said.
"It also means that rehabilitation can start sooner so optimal long-term outcomes can be achieved."
If the patient is suffering other critical injuries they may need to be taken to the nearest hospital for life-saving treatment, and then on to the specialist spinal unit at the three hospitals.
There wouldn't be an increase in the number of spinal patients in those centres, it simply changes the time-frame, Dr Coleman said.
"When you've got a clear policy you can be absolutely sure that people will be treated in the right way."
President of The Association for Spinal Concerns, Gavin Parish, 65, represented the viewpoints of people with spinal injuries and their families during discussions around the policy.
He was injured in a motorbike crash in 2006 on Auckland's North Shore when he was struck by a car driving on the wrong side of the road.
He was taken from the scene of the crash to Auckland Hospital, where he was treated for other serious injuries including broken bones and bleeding for a number of weeks.
He was later taken to Middlemore Hospital, but his spinal cord was severely damaged and he lost the use of his legs.
Mr Parish said under the new policy he would have been taken straight to Middlemore, where there would have been expertise to deal with the other injuries and de-compress his spinal cord.
"It will get [patients] the support they need at that critical period," he said of the new policy.
"There will be all the services available to wrap around the patient, rather than the patient having to move around to get the services they need."
The sooner the rehabilitation can begin, the better for the patient to re-integrate into the community, Mr Parish said.
Dr Coleman said every year there were about 100 new cases of spinal cord injuries and the average age of patients was 34-years-old.
"That patient has 50 years of life ahead of them and you want to make sure you're going to optimise those years," he said.
Forty per cent of new cases were from car crashes, he said.
Minister for ACC Nikki Kaye said the average lifetime costs of a person with a spinal cord injury was between $5 million and $6 million, and for a patient injured under the age of 20 it was $13 million.
Training for ambulance staff has been underway since June, to enable the new approach to take effect from August 1.