The Agency's Bay of Plenty highway manager Niclas Johansson said the new wide centre line would help separate vehicles and reduce the risk of crashes, and increase safety on that stretch of road.
"Since 2009 there has been 15 crashes on this stretch of State Highway 30. Of these, five crashes involved vehicles that had crossed the centre line," he said.
"The extra space in the middle of the road created by the wide centre lines will give motorists more time to react and recover if they make a mistake."
The markings have been successfully trialled at 15 sites around New Zealand as part of Safer Journeys, the Government's road safety strategy.
Mr Johansson said the Transport Agency had studied the trial sites for three years and data indicated that installing a wide centre line would reduce injuries and head-on crashes by 66 per cent and all crashes by 21 per cent.
"The expectation is that this initiative will help to improve safety in the future."