Hank on 6/3/2014 9:35:57 PM:
I would ride the back roads to the Grafton Ferry, cross the Mississippi, then ride to Alton on the Great River Road. From Alton take the Madison County bike trail system down to Chain of Rocks bridge, cross over the Mississippi to the St. Louis Riverfront Trail, then head south to the Arch. Probably not the most direct route but in my mind the best. You could also ride Highway 94 to cross the Alton bridge.