els ▁in ▁the ▁United ▁States , ▁where ▁most ▁t unn els ▁feature ▁a ▁cur ved ▁roof ▁and ▁flat ▁side - w alls . ▁Engine ers ▁borrow ed ▁a ▁European ▁design ▁to ▁give ▁the ▁tunnel ▁added ▁strength . ▁After ▁the ▁can y on ▁wind s ▁past ▁the ▁Book ▁Cl iffs , ▁the ▁highway ▁follows ▁the ▁Colorado ▁River ▁through ▁a ▁valley ▁containing ▁the ▁communities ▁of ▁Par ach ute ▁and ▁R if le . ▁ ▁Glen wood ▁C any on ▁East ▁of ▁the ▁city ▁of ▁Glen wood ▁Spr ings , ▁the ▁highway ▁enters ▁Glen wood ▁C any on . ▁Both ▁the ▁federal ▁and ▁state ▁depart ments ▁of ▁transport ation ▁have ▁pra ised ▁the ▁engineering ▁achiev ement ▁required ▁to ▁build ▁the ▁fre ew ay ▁through ▁the ▁narrow ▁g orge ▁while ▁pres erving ▁the ▁natural ▁beauty ▁of ▁the ▁can y on . ▁A ▁ ▁section ▁of ▁road way ▁features ▁the ▁No ▁Name ▁T unnel , ▁H anging ▁Lake ▁T unnel , ▁Re verse ▁Cur ve ▁T unnel , ▁ 4 0 ▁brid ges ▁and ▁vi ad uct s , ▁and ▁miles ▁of ▁retain ing ▁walls . ▁Through ▁a ▁significant ▁portion ▁of ▁the ▁can y on , ▁the ▁east bound ▁lan es ▁extend ▁cant ile ver ed ▁over ▁the ▁Colorado ▁River ▁and ▁the ▁west bound ▁lan es ▁are ▁susp ended ▁on ▁a ▁vi ad uct ▁several ▁feet ▁above ▁the ▁can y on ▁floor . ▁Al ong ▁this ▁run , ▁the ▁fre ew ay ▁h ugs ▁the ▁north ▁bank ▁of ▁the ▁Colorado ▁River , ▁while ▁the ▁main ▁line ▁of ▁the