Today, the MLK Bridge serves as a relief route for the monumental traffic jams that backup across the downtown Saint Louis river crossings. In fact, one idea to relieve the traffic problems involve putting up a twin span to the MLK, and routing I-70 over the twin spans. Moving I-70 off of the Poplar Street Bridge could really improve Saint Louis traffic.
Update—the Illinois DOT plans to close the MLK bridge between October 12, 2009, and October 24, 2009, to make safety repairs to the MLK bridge. The narrow lanes and the lack of a divider has lead to 38 serious accidents between 2003 and 2009. The bridge will be reconfigured for 2 lanes heading east into Illinois, and one lane heading west into Saint Louis. Converting the bridge to 3 lanes will allow the lanes to be a bit wider and allow for a center divider to be installed.