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Modernized I-29 Unifies Downtown Sioux City

Sioux City, IA

The I-29 project in downtown Sioux City modernized the existing 1960’s-era facility, which had deficient weaving sections, short ramps with abrupt entrances and exits, and horizontal and vertical curves that no longer met standards to squeeze four uncommon interchanges into 3.5 miles. This segment of urban freeway caused safety concerns for state officials, with an accident rate two to four times the statewide average.

Missouri River crossing

The new $276 million project reduces and flattens the I-29 horizontal curves, improves interchange spacing, replaces 13 bridges, makes ramp configurations more consistent with driver expectations, and adds a mainline lane in each direction. The project improved access to and through downtown for all motorists, enhanced access to the riverfront for pedestrians, and replaced thousands of feet of subsurface utilities. These changes have resulted in a facility that connects and unifies the City while improving system reliability and resiliency.

To improve the underlying deficiencies, the project needed to reconfigure access to downtown. Floyd Boulevard was shifted west to lengthen the northbound exit and southbound entrance ramps, which were short and did not meet current criteria. Virginia Street was extended and connected to I-29 to form the second half of a split diamond interchange with Floyd Boulevard, opening access to east downtown.

A direct northbound exit ramp to Nebraska Street that braided over the northbound Virginia Street entrance ramp was added to mitigate a short weave and improve access to downtown from the south. The short, tight Pierce Street southbound entrance ramp was replaced with a connection to the new southbound frontage road, which addressed a short ramp, short weaving section, and other geometric deficiencies. The existing tri-level U.S. 77/Wesley Parkway interchange, which had a high accident rate, was converted to a tight diamond configuration, better aligning with driver expectations.

Further changes to the U.S. 77/Wesley Parkway corridor included the addition of a direct Third Street connection that enhanced downtown access and has contributed to the revitalization of the Third and Pearl Street area, including development of the Hard Rock Casino and other nearby businesses. Other non-interstate improvements included reconstruction of Gordon Drive/IA 12, which has led to revitalization of that corridor as well. Finally, a northbound frontage road was added between U.S. 77/Wesley Parkway and Hamilton Boulevard to address short ramps and move a short weave off the mainline.

The extent of access change in the plan drove dramatic differences in profiles as old bridge openings through the interstate fills were closed, new sideroad connections required bridge approach construction where the interstate was formerly low, and new longer current vertical curve standards were applied that, on their own, would have resulted in a dramatically altered profile. While complicated in their own right, the combination of plan and profile changes drove the engineering excellence and innovation that underpins this project, including large-scale application of expanded polystyrene (EPS) foam fills with fascia panel walls, a straddle bent with an integrally framed pier cap, extensive water main, sanitary sewer trunkline, and large-scale stormwater outfall replacements, as well as comprehensive maintenance of traffic to get it all constructed.

The new $276 million I-29 through Sioux City reduces and flattens the I-29 horizontal curves, improves interchange spacing, replaces 13 bridges, makes ramp configurations more consistent with driver expectations, and adds a mainline lane in each direction. The project improved access to and through downtown for all motorists, enhanced access to the riverfront for pedestrians, and replaced thousands of feet of subsurface utilities. These changes have resulted in a facility that connects and unifies the City while improving system reliability and resiliency.

The project won the Honor Award in the ACEC National competition in partnership with HR Green, the Iowa DOT, and HDR. The project also won the Grand Place Award in the ACEC Iowa competition.

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