The site has been enhanced by Ngai Tahu's Maori Rock Art Charitable Trust and is attracting an estimated 20,000 to 30,000 visitors a year.
They pull off on to small parking areas beside the highway, close to a blind bend.
People parking and then walking across the 100kmh highway have raised safety issues, which the New Zealand Transport Agency hopes to solve with the new car park.
"As visitor numbers, traffic volumes and vehicle speeds have grown, there has been a corresponding increase in concerns and visitor safety," the agency said.
The new car park and picnic area will be on farm land about 70m west of the rock art site. The sealed area will have room for 12 light vehicles and a bus.
It will have a landscaped picnic area with tables and rubbish bins, and a track providing access to the rock art.
The seal for the existing roadside car parks will be removed so vehicles have to use the new parking area. The road is being widened so vehicles can pass those waiting to turn into the car park.
The chance for the car park arose when the trust was about to improve the site entrance, with landscaping and a path.
The site was on the list for safety improvements because, with the entrance close to the curve, visitors crossed the road where there was restricted visibility. Also, tourists often parked on the wrong side of the highway.
