Thanks everyone for the good advice and resources to check.
I have since modified my St Louis to Memphis route to eliminate Tennessee bridge crossings. I will be using ferries from Illinois to Missouri and then from Missouri to Kentucky and continue to Memphis on the east side of the river. (Thanks Terrapax)
However, should anyone be interested, Tennessee sources suggested I use the sidewalks on the I-55 bridge to walk across Ol' Man River. (Thanks for the lead, apneaman).