Just north of an interchange with US 36, the two routes travel over a one-mile-long (1.6 km) viaduct on the banks of the Missouri River.

A portion of the historic Robidoux Row, an area of St. Joseph built by the towns founder, was demolished to make way for the viaduct along the Missouri River.

At roughly the three-quarter point of the viaduct, two sets of exit and entrance ramps, all of which on the eastside of the structure, connect St. Joseph's central business district to the Interstate Highway.

[citation needed] The most dramatic and controversial section of the road is a two-level viaduct (with northbound cars on the top) on the westside of downtown, separating the town from the Missouri River.

[citation needed] More than 400 people gave input on 19 different design proposals through an online survey via the Missouri Department of Transportation's (MoDOT) "I-229: Moving Forward" website.

Proposals in seven different categories included reconstructing the Interstate at-grade or on slightly elevated structures in floodprone areas; removing the top deck and building another elevated structure next to the existing one; decommissioning the Interstate and using local streets or a scenic parkway through downtown St. Joseph; or routing I-229 into Kansas along a 2,700-foot (820 m) long bridge across the Missouri River.

[5] On November 14, 2019, MoDOT told the City of St. Joseph it had settled on two possible alternatives for the two-level section, both of which would involve its demolition and removing the Interstate designation.

According to MoDOT's district planning manager, "Removing the structure and creating a facility that would facilitate local traffic which is what’s going on right now is the best approach moving forward.