 In the early 1970s , AASHTO , the American Association of State Highway Transportation Officials , decided that interstates with a directional suffix , such as I @-@ 80N , would have to be renumbered . By 1974 , I @-@ 80N had been re @-@ designated to I @-@ 680 to match Nebraska . The last piece of I @-@ 680 to be completed in Nebraska was the westbound bridge across the Missouri River . Paving in Iowa wrapped up in the years to come and the entire route was open to traffic by April 21 , 1979 . 
