Anonymous on 6/6/2016 9:01:06 PM:
As CP said you change trains in Chicago. However, assuming you book it as one reservation, you will get one ticket. It will show the two segments, WAS to CHI and CHI to STL. Each will show 1 coach seat or sleeping car accommodation plus 1 bicycle.
In your case since there are several trains from CHI to STL, it won't be a problem. But in general it is best to book it as one reservation, not use the "multi-city" option, because the later connection will not be guaranteed. If the first train is late enough to miss the connecting train, Amtrak takes care of you one way or another.
Also, in general it is better to book a round trip as two reservations. There is no discount for a RT ticket.
Note: on the Capitol limited the bike goes in a rack in the lower leel of a coach-baggage car. From CHI to STL you carry it into the single level coach and stash it in wheel chair space, luggage space, luggage rack, or where ever the conductor directs you. Turning the handlebars sideways facilitates boarding the train and stowing it.