The contractions started getting more intense, so about 5.30am they decided to drive to the hospital.
But about halfway there, Ms Roberton told her husband "the baby's coming".
They pulled over and very soon after that, Mr Roberton said he could see the baby's head crowning.
An ambulance was called but Heidi couldn't wait, and was delivered by her father as her mother lay in the front seat.
"We lay the seat back as far as we could but the baby capsule was behind it.
"Once I got my head together, training kicked in, and I was speaking with one of the call-takers at the St John medical centre as well," Mr Roberton said.
He had some "basic" first aid equipment, but had to use the baby's new rug to wrap her in when she was born.
"It's pretty wrecked now, I'd say."
There were no complications with the birth of the 3.5kg baby, he said.
The ambulance arrived 10 minutes later and took them all to the hospital.
Midwife Frances Kissling said it was very unusual for a first child to arrive so quickly. "Usually these first wee babies don't arrive with such great gusto. But a great outcome, which was lovely."
She said the Robertons did all the right things.
"But it just goes to show how amazing women are and the process of birth is - mother nature, when we leave it alone, does a really good job.
"It just happened as it was meant to, albeit unexpected, but the process itself was wonderful. They couldn't have had a better outcome."
Mr Roberton said it was a pretty good story and reckoned it would be a good one to tell at his daughter's 21st.
-APNZ
