The Missouri South Interchange, a reconfiguration of the Missouri approach to the Poplar Street Bridge, is one of the many deferred components of the Mississippi River Bridge project currently under construction. With the rerouting of I-70 across the new bridge, the ramps that connect the depressed section to the Poplar Street Bridge and Illinois will become redundant. To take advantage of this redundancy, MoDOT would like to remove the I-70 ramps so that the ramps connecting to I-55 can be expanded from one to two lanes each way, a change that could do much to ease the existing congestion.
One aspect of the Missouri South Interchange, however, needs further review, especially in light of the recent publicity and support garnered by the citizen group City to River. As presented in the 2001 draft environmental impact statement (DEIS), one portion of the Missouri South Interchange would involve elevating and extending Spruce St over southbound Memorial Drive and the depressed section to a realigned Poplar St and northbound Memorial Drive. Positively, an extended Spruce St would improve connectivity between southern downtown and the Arch grounds; negatively, Memorial Drive would become even more of a traffic sewer than it is now, a moat dividing downtown from the Arch. The city of St. Louis needs to decide what it wants Memorial Drive to be—a street for people or a street for cars.
Considering the age of the DEIS, updates will need to be made to account for changes to the built environment should the Missouri South Interchange ever get implemented. For example, the new 6th St onramp to eastbound I-64 obviates the need for an onramp directly from Broadway. A description of the proposed changes associated with the Missouri South Interchange can be found in Chapter 3 of the Mississippi River Crossing DEIS:
The directional ramps to the bridge in Missouri will be revised to better accommodate the remaining I-55/64 movements, once the I-70 movements are relocated to the new bridge. The existing two-lane east- and westbound I-64 movements will be retained, and the one-lane north- and southbound I-55 movements will be upgraded to better-design-standard two-lane movements. […]
The northbound I-55 exit ramp to northbound Memorial Drive will be relocated to provide better exit ramp spacing; the northbound I-55 exit ramp movement to eastbound Poplar Street will be removed. Local (downtown) access presently provided from north- and southbound Memorial Drive will be relocated. A westbound I-64 off-ramp will be provided to Fourth Street at Spruce, and an eastbound I-64 on-ramp will be provided to from southbound Broadway immediately south of Spruce. These improvements will require making Spruce Street one-way westbound between Fourth and Broadway, vacating Poplar Street between Fourth and Broadway, and placing a cul-de-sac on Poplar Street immediately west of Broadway. […]
The Missouri Poplar Street Bridge approach modifications will include connecting Spruce Street at Fourth Street over southbound Memorial Drive and the interstate to a new intersection with two-way Poplar and northbound Memorial Drive. A southbound Memorial Drive tie-in will connect to the elevated Spruce Street, and a local access leg of southbound Memorial Drive will extend from the beginning of the southbound I-55 on-ramp to Fourth Street on the south side of the Sverdrup Plaza building. These improvements will permit two-way circulation around the Gateway Arch grounds, as well as link the south side of downtown (and its interstate access) with the Arch grounds for both motorists and pedestrians.