 The first section of I @-@ 80 to open for traffic , 2 1 ⁄ 2 miles ( 4 @.@ 0 km ) from the West Mixmaster to the Douglas Avenue interchange in Urbandale , opened on September 21 , 1958 . By the end of November 1959 , the new interstate extended around the north side of Des Moines to US 69 . Within a year , the East Mixmaster , where I @-@ 35 splits away to the north , was opened . By the end of 1960 , 40 miles ( 64 km ) from US 71 north of Atlantic to US 6 near Dexter , 20 miles ( 32 km ) from I @-@ 35 to US 6 west of Newton , and 28 miles ( 45 km ) from Iowa 38 near the Cedar River to US 61 in Davenport had opened to traffic . 
