ers ▁scra pped ▁the ▁original ▁plans ▁and ▁started ▁work ▁on ▁a ▁new ▁design ▁that ▁would ▁minim ize ▁additional ▁environmental ▁impact s . ▁A ▁new ▁design ▁was ▁under way ▁by ▁ 1 9 7 1 , ▁which ▁was ▁approved ▁in ▁ 1 9 7 5 ; ▁however , ▁environmental ▁groups ▁file d ▁law su its ▁to ▁stop ▁construction , ▁and ▁the ▁controvers y ▁continued ▁even ▁when ▁construction ▁finally ▁res umed ▁in ▁ 1 9 8 1 . ▁The ▁final ▁design ▁included ▁ 4 0 ▁brid ges ▁and ▁vi ad uct s , ▁three ▁additional ▁tunnel ▁b ores ▁( two ▁were ▁completed ▁before ▁construction ▁was ▁stopped ▁in ▁the ▁ 1 9 6 0 s ) ▁and ▁ ▁of ▁retain ing ▁walls ▁for ▁a ▁stretch ▁of ▁fre ew ay ▁ ▁long . ▁The ▁project ▁was ▁further ▁complicated ▁by ▁the ▁need ▁to ▁build ▁the ▁four - lane ▁fre ew ay ▁without ▁disturb ing ▁the ▁operations ▁of ▁the ▁rail road . ▁This ▁required ▁using ▁special ▁and ▁coordin ated ▁bl ast ing ▁techniques . ▁Engine ers ▁designed ▁two ▁separate ▁tracks ▁for ▁the ▁highway , ▁one ▁elev ated ▁above ▁the ▁other , ▁to ▁minim ize ▁the ▁foot print ▁in ▁the ▁can y on . ▁The ▁final ▁design ▁was ▁pra ised ▁for ▁its ▁environmental ▁sens itivity . ▁A ▁Den ver ▁architect ▁who ▁helped ▁design ▁the ▁fre ew ay ▁proc laimed , ▁" M ost ▁of ▁the ▁people ▁in ▁western ▁Colorado ▁see ▁it ▁as ▁having ▁preserved ▁the ▁can y on ." ▁He ▁further ▁stated , ▁" I ▁think ▁pieces ▁of ▁the ▁highway