The project involves expanding the two-lane road’s width from nine metres to 12 metres along the 80km from Nan Muang district to Ban Huay Kon in Chalermphrakiat district, near the border with Laos.
About 1,000 trees have been cleared from the route. The protests, Mr Prachan said, mostly involve the tunnel of trees.
Residents and civic groups in Nan last month launched a “love the trees” campaign in the belief it would sway the department and stop the felling, even though the road project is aimed at economic growth for the province.