NZTA regional performance manager Mark Owen said applying chip seal was a very fine balancing act.
"From time to time there will be some instances where, despite our best efforts, the chip does not adhere as well as it should."
Mr Owen said NZTA was aware of the poor condition of chip seal at this location, and had put signs in place warning motorists to take care.
He said they were also regularly sweeping the road to help prevent further damage from loose chips.
"We will be fixing the road surface at the earliest possible opportunity, but we need to wait for an extended spell of warmer and drier weather to ensure the repairs are of a high enough quality to go the distance," said Mr Owen.
"While Mr Schoenbrunn has not approached us with his concerns, we're sorry to hear that his windscreen has been unfortunately damaged on two occasions.
"We encourage people to get in touch with us with any concerns as soon as possible, as we can then take action promptly to reduce the risk of recurrences," Mr Owen said.
Mr Schoenbrunn said he and his wife suffered a smashed windscreen in March, which had to be completely replaced, and another cracked windscreen a few weeks ago, but that one could be repaired.
"In all of our cases oncoming traffic propelled the chips and caused damage despite our own moderate speeds and my defensive driving," he said.
Mr Schoenbrunn was aware warning signs on either end of the problem section of road had been erected, but said a lower speed limit should have been placed on the road.