 As I @-@ 80 and US 6 approach the Quad Cities metropolitan area , the speed limit drops to 65 mph ( 105 km / h ) for the final time . Just within the city limits of Davenport is the I @-@ 280 interchange . US 6 exits to the south to join I @-@ 280 while I @-@ 80 is joined by US 61 . I @-@ 80 and US 61 only share 5 miles ( 8 @.@ 0 km ) of freeway before US 61 exits to its own freeway heading north . In between the two exits is an interchange with Northwest Boulevard , which marks the eastern end of Iowa 130 . A couple miles east of the eastern US 61 interchange is the western end of I @-@ 74 . Because of a " turn off to stay on " interchange with I @-@ 74 and I @-@ 280 near <unk> , Illinois , called " the Big X " , I @-@ 74 through traffic is urged to use I @-@ 80 around the Quad Cities to the Big X. At the Big X , traffic from both I @-@ 74 and I @-@ 80 must exit their respective freeways to continue on the same route . Near the Mississippi River , the interstate takes a sharp curve to the southeast to line up perpendicularly to the river . Just before the base of the bridge is an interchange with US 67 , the last exit in Iowa . I @-@ 80 ends its 306 @-@ mile @-@ long ( 492 km ) journey through Iowa over the Mississippi River on the Fred Schwengel Memorial Bridge . It enters rural Rock Island County , Illinois , and continues towards Chicago . 
