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I-35 Diverging Diamond Interchange

The E. 1st Street Interchange Project includes the design and construction of a diverging diamond interchange (DDI) on I-35 in Ankeny, Iowa.  The project includes the reconstruction of two I-35 bridges over Fourmile Creek, two I-35 bridges over E. 1st Street, and the widening and overlay of the E. 1st Street bridge over Fourmile Creek east of I-35.

The improvements are due to increased traffic volumes, a high rate of severe/fatal crashes on this portion of I-35, and the need for additional capacity on I-35 as a result of a new interchange constructed two miles north at NE 36th Street.

Iowa’s Second DDI

The E. 1st Street Interchange Project will be the second DDI in the state of Iowa. A DDI was selected over other alternatives due to its efficiency of safely moving large volumes of directional traffic, as well as its ability to minimize the footprint of the interchange. Because Fourmile Creek is a sensitive urban stream, culverts and bridges are designed in accordance with DNR and DOT requirements to reduce upstream flooding. An Environmental Assessment is required to permit the reconstruction of a diamond interchange to a DDI configuration as well as accommodate a minor realignment of I-35 north of E. 1st Street.

Due to high traffic volumes on I-35 and E. 1st Street, a detailed staging design is needed to allow continuous traffic movements that are appropriate for the traffic volumes on roadways, while keeping the public and contractors safe during construction. The project is a collaborative effort between the City of Ankeny and the Iowa Department of Transportation.

Snyder & Associates is the primary design consultant responsible for improvements associated with roadways and ramps, while Shuck-Britson, Inc. is the lead structural designer for bridges and box culverts. Snyder & Associates is also facilitating coordination with utility owners and completing required platting and permits.

View the full DDI project write-up to learn more. For additional information on DDI benefits, click here.