 South of Bertram , the two routes cross the Cedar River before US 151 splits away from US 30 to the north at a trumpet interchange . This interchange is the southern end of Iowa 13 . It continues east towards Mount Vernon , two miles ( 3 @.@ 2 km ) west of which , the four @-@ lane highway becomes a two @-@ lane road . In Mount Vernon , it intersects Iowa 1 at a roundabout . One mile ( 1 @.@ 6 km ) from Iowa 1 , it enters Lisbon . 
