First, do the Adventure Cycling maps give a route? I don't know because we did our trip before they were published.
We used a route in Tod Rodger's Bicycle Guide to the Lewis & Clark Trail
The author has helpfully put a copy of the book on-line so you can browse it before ordering. By going to http://www.deerfootpublications.com/chapters/05wb.pdf
, you can see his directions for getting from the St. Louis Airport to St. Charles.
It was very nice of him to make the book available on-line. You could print the whole book out for free, or at least for just the cost of the paper. But, that's really stealing. Buy the book! And, if you'd like to have daily route sheets, you can print them off the computer. This way you don't have to tear up the book.
I haven't tried to compare the book route to the Adventure Cycling Route.
There was some road construction going on when we went from the airport to St. Charles. Things could be different. And I think we scratched our heads a few times, but you ought to be able to make it. I don't see anything in the updates. Traffic wasn't a problem.
We found the book useful for our trip even though our trip was sagged by a commercial touring company. It was nice to have an idea about what could be found in the little town.
Have a good trip.