All national highways shall vest in the Union, and for the purposes of this Act "highways" include--
         (i) all lands appurtenant thereto, whether demarcated or not;
         (ii) all bridges, culverts, tunnels, causeways, carriageways and other structures constructed on or across such highways; and
         (iii) all fences, trees, posts and boundary, furlong and milestones of such highways or any land appurtenant to such highways.