Traffic south of Marcus is about to look a whole lot different — and the clock is ticking on the next big change at the Iowa Highway 3 and 143 construction zone.
The Iowa Department of Transportation says work on the new roundabout near Marcus is moving steadily through phase three of the six‑phase project. And in roughly two weeks, drivers will see one of the most significant shifts yet: Highway 143 will close, cutting off direct access into and out of Marcus while crews move into the next stage of construction. A marked detour will route traffic onto nearby county roads.
DOT Transportation Planner Sarah Tracy says the closure is necessary to keep crews safe and maintain progress on what will become one of Iowa’s largest single‑lane roundabouts — a wide‑diameter design built specifically to handle semis, farm machinery and other large vehicles that frequently use the corridor. She says the project remains on schedule for completion in November, weather permitting.
Safety remains the driving force behind the redesign. The intersection has a long history of severe crashes, including a 2020 collision that killed 26‑year‑old Alexa Brewster of Cherokee. Tracy says roundabouts have proven to reduce serious and fatal crashes by up to 70–80 percent by eliminating high‑speed right‑angle impacts common at rural two‑way stops.
The Marcus roundabout has been in development for several years, and DOT officials have been working with local schools and community groups to help drivers understand how to navigate the new layout once it opens. Demonstrations with model vehicles and farm equipment have been part of that outreach.
For now, drivers should expect shifting traffic patterns, construction crews working close to the roadway and temporary closures on nearby county roads as the project advances. Highway 3 will remain open through most of the construction period, but the upcoming Highway 143 closure will be the biggest change yet — and one the DOT says is essential to keeping the project on track.
The DOT plans to move into phase four shortly after the closure, with all six phases expected to wrap up by late fall.
