I've seen similar tunnels on logging roads where I live near Portland, Oregon. The trees are cut/cleared to make way for the roads, and branches are cut back to keep it clear. Gradually, the tree branches grow over the road/track forming this emerald tunnel. Think of a tree-lined street. The only difference is that the vegetation is less dense on a city street. When a road/track is cut through a forest, these tunnels are formed naturally.