Emergency services attended but she died at the scene.
Detective Guy Jackson of Taranaki CIB said: "Mrs Fairweather was being a good Samaritan and went to move the frames which had stupidly been put in the middle of a major highway.
"However, due to the atrocious weather and heavy rain, a northbound vehicle has struck her. The driver of this vehicle is understandably traumatised from the crash and we are continuing to speak to them."
Police were seeking witnesses who may have seen the barriers placed across the road.
"We are continuing to make inquiries and speak to witnesses and we want to speak to anyone who either stopped at the scene at the time of the crash or who may have seen the barriers being placed on the road," Mr Jackson said.
"If anyone saw any suspicious behaviour or something just out of the ordinary in the area, please contact police.
"I also want to take this opportunity to encourage those who put the barriers on the road to do the right thing and come forward."
Anyone with information is asked to call Mr Jackson on (06) 215 5263 or the anonymous Crimestoppers line on 0800 555 111.