Complex sentence: The airport which was built in the Missouri River bottoms was also built next to the rail tracks at the Hannibal Bridge at a time when air travel was thought was going to be used in conjunction with rail traffic.
Split into simpler sentences: The airport which was built in the Missouri River bottoms was also built next to the rail tracks at the Hannibal Bridge. At a time when air travel was thought was going to be used in conjunction with rail traffic.