Drivers heading into Marcus will see a major change this week as the Iowa Department of Transportation closes Iowa Highway 143 at its intersection with Highway 3.
The closure marks the start of the final phase of construction on the new single‑lane roundabout — a project the DOT says is designed to improve safety at one of northwest Iowa’s most crash‑prone rural intersections.
The shutdown of 143 is expected to last until the end of October, weather permitting. During that time, Highway 3 will remain open, but only in a single lane controlled by temporary traffic lights. The DOT says motorists should expect delays, lane‑width restrictions of 10 feet and a height limit of 15 feet. Cherokee County Road L36 will also stay closed until the project wraps up.
Drivers will need to follow a marked detour using County Roads C38, L22, C16 and L40 to reach Marcus. DOT officials say the detour is necessary to keep crews safe as they complete the final construction steps on what will be one of Iowa’s largest single‑lane roundabouts — a wide‑diameter design built to accommodate semis, farm machinery and other large vehicles that frequently use the corridor.
The roundabout project has been years in the making. DOT District 3 Transportation Planner Sarah Tracy has previously said the redesign is driven by safety concerns, noting the intersection’s history of severe crashes, including a 2020 collision that killed a 26‑year‑old Cherokee woman. National research from the Federal Highway Administration shows modern roundabouts can reduce serious and fatal crashes by 70-80 percent by eliminating high‑speed right‑angle impacts.
The DOT has spent the summer working with schools, community groups and local drivers to help residents understand how to navigate the new layout once it opens. Demonstrations with model vehicles and farm equipment have been part of that outreach.
As construction enters its final stretch, the DOT is reminding drivers to slow down, obey posted signs and stay alert in the work zone. Traffic fines for moving violations are doubled in construction areas. The agency also encourages motorists to check Iowa 511 for real‑time updates on closures, delays and detours.
If the schedule holds, the roundabout is expected to be completed by late fall.
