A covered bridge is a great feature on any American based railroad: Google earth or a satellite view can be helpful to place a bridge in the location where it looks realistic.
One factor to consider, however, is track cleaning. No problem if you operate with battery power but track power will mean easy access to the track within the bridge.
When I built a truss type bridge I made it removable (this is not obvious to the eye). This not only allows for easy track cleaning and maintenance but also allows for repaints and other work that will be needed over a period of time.
Mention was made of clearances for rolling stock. Dependant on your railroad empire - you may have sufficient stock already - but a change of modeling interests could mean problems at a later date.