New Tower Terrace interchange at I-380 to open this month

The new Interstate 380 interchange at Tower Terrace Road in Cedar Rapids and Hiawatha is expected to fully open later this month.

A ribbon-cutting ceremony for the new interchange — a “diverging diamond” design — is scheduled for June 22, and the Iowa Department of Transportation is hoping to have the roadway’s on and off ramps open on or shortly after that date, according to Catherine Cutler, Iowa DOT transportation planner in the District 6 office in Cedar Rapids.

This will be Iowa’s third diverging diamond interchange, and the first on the east side of the state. Diverging diamond is an interchange design in which traffic switches to the left side of the roadway while crossing over the interstate, allowing those turning left onto the interstate a clean turn, rather than turning across incoming traffic.

The other two completed diverging diamonds in Iowa are near Waukee, opened in 2015, and in Ankeny, opened in 2020. More diverging diamond interstates are planned in Iowa, including one at the intersection of Interstate 80 and First Avenue in Coralville and one on I-380 and Boyson Road in Cedar Rapids.

The Iowa DOT decided to use a diverging diamond interchange on Tower Terrace because it takes up less land than other options, and has proved to be safer than a traditional interchange. National studies show diverging diamond interchanges reduce crashes by 37 percent and fatal and injury crashes by 54 percent, according to Cutler.

“It’s just the idea that you’re going to cross over traffic that freaks people out at first,” Cutler said.

Diverging diamond interchanges are “very common in Missouri. They’re very common on the East Coast. It’s just that we only have two and this will be the third one in Iowa. I think once people drive through them, it’s intuitive and everybody will be fine. They improve safety over regular interchanges because when you’re making that left turn, you don’t have to gauge that oncoming traffic. You’ll just have a free-flowing left.”

The new Tower Terrace interchange cost about $22 million, with about $5 million coming from local municipalities. Cedar Rapids and Hiawatha each contributed about $2.2 million, and Marion, Robins and Linn County each contributed about $200,000, according to Cutler. The federal government paid most of the cost, with the state also contributing.

While the interchange itself only affects Cedar Rapids and Hiawatha, it is part of a larger, ongoing Tower Terrace project, which hopes to expand Tower Terrace Road to connect I-380 on the west to Highway 13 on the east. When finished, the road will span 8.3 miles through Cedar Rapids, Hiawatha, Robins, a portion of unincorporated Linn County and Marion.

The larger Tower Terrace project is currently estimated to be finished in 2045, but could be finished sooner if additional funding can be acquired through a federal grant.

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