"They were lucky. They all managed to clamber out," said Mr Howard.
He said it was apparent from markings on the road they would have slid along the road upside-down for several metres.
"They are quite lucky to walk away from it. It was upside-down for quite a while."
Mr Howard said the three received only bumps and scratches but the car was a bit of a mess. "It could have been quite bad."
He did not know if they were from Wairarapa but believed they had been on their way to the Tora Tora Tora music festival.
A woman who had stopped to help them drove them to Wellington after they had been assessed by Wellington Free Ambulance staff.
Police also attended and a fire crew managed traffic control.
No other vehicles were involved in the crash.