Plant

This sign greeted me up at Scenic world in Katoomba. It is somewhat confusing, I must admit. What do they actually mean by "road plant ahead"? Is it a factory that makes roads? Or a plant that grows roads, in which case I've been sorely mistaken on the subject of how roads are made... Do they mean to tell me there's a road ahead that is not the road it looks like; that it was put there as a "plant"? Or is there a plant growing in the road?

These are the things that keep me awake at night.