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New design coming for busy I-70 interchange in St. Charles

Mapbox, OpenStreetMap
The Fifth Street Interchange is the first I-70 exit west of the Missouri River. It's currently a partial cloverleaf design.

The first I-70 interchange west of the Missouri River is getting an $18 million update. Construction starts next spring to replace Fifth Street’s partial cloverleaf interchange with a diverging diamond.

It’s the latest project in a decade-long plan to improve the main corridor through the St. Louis region’s fastest growing county.

“This section of I-70 is one of the busiest sections of I-70 across the whole state," said John Greifzu, transportation director for St. Charles County. “And this interchange, which was designed back in the 1970s, has just become outdated and needs some work to make it operate more efficiently.”

Fifth Street is the exit to the Ameristar Casino, Bass Pro Shops and other stores and businesses. It leads into the city of St. Charles. Greifzu said the existing interchange makes drivers change lanes and can lead to aggressive driving when there’s a lot of traffic.

“We get quite a few complaints from folks that it just doesn’t feel safe. The congestion’s got to a level that with the gaps in traffic they’re having to make some questionable calls and cut folks off,” Greifzu said.

The city of St. Charles and St. Charles County are splitting two-thirds of the bill for the project, about $6.5 million each. The county funds come from its half-cent transportation tax. The East-West Council of Governments is providing almost $4 million in federal money, and the Missouri Department of Transportation is providing the final $1 million and overseeing the project.

An open house explaining how the new interchange will work, as well as traffic flow during construction, will be held at the St. Charles Administration Building, 201 N. Second Street, on Thursday from 4 to 6 p.m.

Follow Camille Phillips on Twitter: @cmpcamille.