 For the next 50 miles ( 80 km ) , I @-@ 80 runs in more or less a straight line . Interchanges occur at regular intervals ; 3 to 6 miles ( 5 to 10 km ) of Pottwattamie and Cass county farmland separate each exit from the next . Near Avoca , it crosses the West Nishnabotna River and meets US 59 . East of the interchange , the interstate crosses the eastern branch of the West Nishnabotna . As I @-@ 80 approaches the area north of Atlantic , there are three interchanges , Iowa 173 , County Road N16 ( CR N16 ) , and US 71 , which serve the western , central , and eastern parts of the city , respectively . Iowa 173 , which serves Atlantic by way of Iowa 83 , also connects to Elk Horn and Kimballton . US 71 , which continues north towards Carroll , carries US 6 traffic to the interstate . At this point , US 6 begins the first of three instances when its traffic is routed along I @-@ 80 . In the eastern part of Cass County , the two routes meet the northern end of Iowa 148 . 
