During the 1950s, as today's highway system was beginning to take shape, Iowa 150 was rerouted a couple times in Cedar Rapids. The first adjustment happened in 1954, when US 30 was taken off of Mount Vernon Road and put onto a new road on the south side of town. Iowa 150 was moved west through downtown and across the Cedar River. It turned south onto 6th Street SW, on which US 30 and US 218 joined at 18th Avenue SW. The three routes turned east onto the new road, but US 218 turned south at Bowling Street SW. Within five years, Iowa 150 moved to the northeast side of Cedar Rapids and into Marion. Instead of continuing south to Coe College, it turned east at Collins Road and connected with US 151 and Iowa 64 near the eastern city limits. It then followed those two routes to downtown Marion, where it turned south onto a road which headed southeast towards Mount Vernon. East of Mount Vernon, it followed US 30 to Iowa 38 and continued towards Davenport. Within a few years, Iowa 150 was rerouted onto the newly extended Iowa 13, which was extended south to US 30 near Bertram. At its longest extent, the route was long.