One turn-around point if I were driving south across the Chouteau bridge would be to travel south across, turn right on N. Chouteau Trfy, head back N. along the W side of Chouteau, turn right to go under bridge, take my first right S. on Chouteau Bridge Rd then back north on Chouteau.
If traveling S. across the I-435 bridge, Front Street would be my 1st choice there.
I've noted both of those travel points as they both cross the river (driving).
Walking...
There is a void between the lanes of traffic on the Chouteau bridge, and only chain link fencing not meant to walk on, but placed between the lanes of travel to protect anyone from falling to their death.
I would never want to even stop my vehicle on the I-435 bridge in fear of getting rear ended, and certainly not walk on it because there are no shoulders. . Once again, 65mph zone.