The Lewis & Clark Memorial Bridge was built for the Interstate Highway program. I-90 was built though South Dakota in the early 1970s. The US-16 bridge was considered for the river crossing, but was soon rejected because it would have required running I-90 through the city of Chamberlain. A new bridge was needed on a new alignment. The result was the current 2,031 foot long structure with an equally long causeway on the west side of the crossing, for a total project length of nearly a mile.
The bridge is a very economical steel girder structure. It was built for minimal cost, which explains why it has no decorative features. Had the bridge been built today, it would have been built with modern guardrails, a larger divider in the middle, wider lanes, full width shoulders, and more distance between the two sets of lanes. While that might have been ideal, the current bridge is in good condition, and simply doesn't warrant the cost of replacement.